ELECTRICAL SYSTEMS - GENERATORS

POWER GENERATION

Generators play an important part in your assignment with the Seabees. Whether operating a generator as a main power source or as standby power or as emergency power, you need a through knowledge of their hookup, operation, and maintenance. At the completion of this chapter, you should know how to install generators of the advanced-base type, stand a generator watch, perform preventive maintenance, and make minor repairs on power generators and control equipment. Theory for both dc and ac generators is included in Navy Electricity and Electronics Training Series (NEETS), Module 5. Generator theory will not be covered in this chapter. Keep in mind that the generator (alternator) in an automobile works on the same principle as does the huge turbine generator used in a nuclear power station.

INSTALLATION AND SERVICING GENERATORS

Most of the generators you are likely to work with in the Naval Construction Force (NCF) range in size from 5 kW to 200 kW. Generators in these sizes range in weight from 488 pounds (221.4 kg) to 10,500 pounds (4770 kg). All of these units are mounted on skid bases. Lifting and tie-own attachments are provided. All have provisions for lifting with a forklift of the appropriate capacity (with the exception of the 5-kW gas-driven generator set, which does not include the forklift provision). Several factors should be considered before a final decision is made about where to locate a generator. The noise levels of generators sized from 5 kW to 200 kW range from 77 dBa to 93 dBa (adjusted decibels) at 25 feet. Generator noise is a problem in low-noise level or quiet areas (libraries, offices, hospitals, chapels, etc.).

The operating 60-kW generator, for example, presents a noise hazard (84 dBa to 91 dBa, depending on the model) to all personnel in the immediate area. The noise level near the unit exceeds the allowable limits for unprotected personnel. Therefore, everyone working around the generator needs single (noise < 84 dBa) or double hearing protection (noise > 104 dBa).

Placing a generator set near points of large demand will reduce the size of wire required, hold the line losses to a minimum, and afford adequate voltage control at the remote ends of the lines.

The following points should be considered before an exact site is chosen for a generator set:

1. Generators must not be closer than 25 feet (7.6 meters) to a load because of noise, fire hazard, and air circulation.

2. The set must be placed on a stable, preferably level, foundation. It should not be operated while inclined more than 15 degrees from level.

3. The site must be within 25 feet (7.6 meters) of any paralleled generator set and within 25 feet (7.6 meters) of any auxiliary fuel supply.

4. When preparing a temporary installation, you should move the generator set as close to the jobsite as practical. In an area where the ground is soft, do not remove the wood-skid base if you have not already done so. The wood-skid base will establish a firm foundation on soft ground, mud, or snow; otherwise, use planks, logs, or other material for a base in an area where the ground is soft.

Although advanced-base portable generators are designed to be operated outdoors, prolonged exposure to wind, rain, and other adverse conditions will definitely shorten their lives. When the generators are to remain on the site for any extended period of time, they should be mounted on solid-concrete foundations and should be installed under some type of shelter.

There are no predrawn plans for shelters for a small advanced-base generating station. The shelter will be an on-the-spot affair- the construction of which is determined by the equipment and material on hand plus your ingenuity, common sense, and ability to cooperate with personnel in other ratings. Before a Builder can get started on the shelter, you will have to furnish information, such as the number of generators to be sheltered, the dimensions of the generators, the method of running the generator load cables from the generator to the panelboard and from the panelboard to the feeder

Typical 60-kW generator set.

system outside the building, and the arrangement of the exhaust system. Large generator units may have, connected or attached to them, engine equipment that requires extra space and working area. Included in this equipment are air-intake filters, silencers for air intake and exhaust, fuel and lubricating oil pumps, tanks, filters, and strainers. Also included are starting gear, isochronous regulating governors with over-speed trips, safety alarm and shutdown devices, gauges and thermometers, turning gear, along with platforms, stairs, and railings.

An even larger and more complete power plant may require separate equipment, such as a motor-driven starting air compressor and air storage tanks; motor-driven pumps for jacket water and lubricating oil cooling, or heat exchangers with raw cooling water pumps and lubricating oil coolers; and tanks that include day-fuel storage.

Be sure to provide enough working space around each unit for repairs or disassembly and for easy access to the generator control panels. Installation specifications are available in the manufacturer's instruction manual that accompanies each unit. Be sure to use them. Consulting with the Builder about these specifications may help cut installation costs and solve future problems affecting the shelter of the generator.

SERVICING THE GENERATOR

Before the set is operated, it must be serviced. We will use the 60-kW generator set as an example for discussing the servicing of the set after you receive it.

As you read this discussion, refer to figure for locating fill and drain points and drain valves.

Batteries All 5-kW through 750-kW generator sets are furnished with dry-charged batteries less the electrolyte. Battery electrolyte must be requisitioned separately.

You must be cautious when installing, activating, or maintaining batteries. Before we discuss connecting WARNING Do not smoke or use an open flame in the vicinity of batteries when servicing them. Batteries generate hydrogen a highly explosive gas. When removing batteries, always remove both negative cables before removing the positive cables .

Battery electrolyte contains sulfuric acid and can cause severe burns. It is highly toxic to the skin, eyes, and respiratory tract. Skin, eyes, and face (chemical splash goggles, face shields) and respiratory protection are required. Whenever electrolyte comes into contact with the body, the eyes, or the clothing, you must rinse immediately with clean water, remove contaminated clothing, and then go to sickbay or the medical clinic for a thorough examination. The 60-kW generator set is equipped with two 12- volt, 100-ampere-hour batteries. The batteries are located under the radiator on aroll-out tray . They are connected in series to supply 24 volts dc for starting the generator set and operating direct current components. Two slave receptacles, connected in parallel, permit easy connection to the batteries to supply or obtain battery power. As we and servicing batteries, let's look at a few safety points you must know about.

Figure.- Battery cable connections and slave receptacles.

discuss activating the batteries, refer to steps 1 through 3 (following) and figure

1.Open the battery compartment door and secure it to the radiator grille with the door holder. SPECIFIC GRAVITY DESIRED USING 1.835 SPECIFIC USING 1.400 SPECIFIC GRAVITY ACID GRAVITY ACID PARTS OF PARTS OF PARTS OFPARTS OF WATER A C I D WATER ACID

2. Depress the button on top of the quick-release pins, lift up the pins, and pull the roll-out tray assembly out.

3. Remove the filler caps. When you have electrolyte of the correct specific gravity, do not dilute it, but fill the battery cells to the cell slots.

When you prepare your own electrolyte, consult a mixing chart (table). In this case, use the specific gravity value recommended in the instruction manual.

Table.- Electrolyte Mixing Chart

The temperature of the electrolyte when placed in the cells should be between 60° F and 90° F. IT SHOULD NEVER EXCEED 90° F.

A chemical reaction occurs when you add electrolyte to the battery, thereby causing the battery to heat. Cool it artificially (cooling fans) or allow it to stand at least 1 hour before placing it in service.

WARNING Be sure to add the acid to the water s-l-o-w-l-y, stirring constantly and thoroughly.

Figure.- Battery compartment.

You will notice at the end of the cooling period that the level of the electrolyte has dropped because of the electrolyte soaking into the plates and separators. Before placing the battery in service, restore the electrolyte to its proper level. Remove any electrolyte spilled on the battery, using a cloth dampened with a solution of bicarbonate of soda and water.
Although you can place the battery in service 1 hour after filling it with electrolyte, do so only in an emergency. If at all possible, give the battery an initial light charge.

After the battery has been charged, connect the battery into the starting system of the prime mover, as shown in figure. Always connect the negative cable last.

4. Push in the roll-out tray assembly and install the quick-release pins .

Battery Charging

The manufacturer's manual may specify charging procedures for the type of battery you are to charge. If so, follow those procedures.

There are several types of battery charges, but you will generally use a normal charge, an equalizing charge, or a fast charge. We will discuss these three types of charges briefly. For more information on storage or dry-cell batteries and battery charging, refer to the Navy Electricity and Electronics Training Series (NEETS), NAVEDTRA 172-01-00-88 (Module 1).

NORMAL CHARGE.- A normal charge is a routine charge that is given according to the battery nameplate data during the ordinary cycle of operation to restore the battery to its charged condition,

EQUALIZING CHARGE.- An equalizing charge is a special extended normal charge that is given periodically to batteries as part of a maintenance routine. It ensures that all the sulfate is driven from the plates and that all the cells are restored to a condition of maximum specific gravity. The equalizing charge is continued until the specific gravity of all cells, corrected for temperature, shows no change for a 4-hour period.

FAST CHARGE.- A fast charge is used when a battery must be recharged in the shortest possible time. The charge starts at a much higher rate than is normally used for charging. It should be used only in an emergency, as this type of charge may be harmful to the battery.

CHARGING RATE.- Normally, the charging rate of Navy storage batteries is given on the battery nameplate. If the available charging equipment does not have the desired charging rates, the nearest available rates should be used; however, the rate should never be so high that violent gassing occurs.

CHARGING TIME.- The charge must be continued until the battery is fully charged. Frequent readings of specific gravity should be taken during the charge and compared with the reading taken before the battery was placed on charge.

GASSING.- When a battery is being charged, a portion of the energy breaks down the water in the electrolyte. Hydrogen is released at the negative plates and oxygen at the positive plates. These gases bubble up through the electrolyte and collect in the air space at the top of the cell. If violent gassing occurs when the battery is first placed on charge, the charging rate is too high. If the rate is not too high, steady gassing develops as the charging proceeds, indicating that the battery is nearing a fully charged condition.
WARNING A mixture of hydrogen and air can be dangerously explosive. No smoking, electric sparks, or open flames should be permitted near charging batteries.

CHARGING PROCEDURE.- If the instruction manual for the generator set is not available or if it does not give the battery a charging procedure, proceed as follows: Connect the positive battery charger terminal to the positive battery terminal and the negative charger terminal to the negative battery terminal.

Charge the battery at a low rate (about 5 amperes) until the voltage and specific gravity, corrected to 80° F (27° C) remains constant for at least 4 hours. If the temperature of the electrolyte reaches 110° F (43° C), reduce the charging rate or stop the charge until the battery cools. NEVER PERMIT THE TEMPERA-TURE TO EXCEED 115° F (46° C). During the charging, replenish any water lost by evaporation.

Hydrometer A hydrometer is the instrument used to measure the amount of active ingredients in the electrolyte of the battery. The hydrometer measures the SPECIFIC GRAVITY of the electrolyte. Specific gravity is the ratio of the weight of the electrolyte to the weight of the same volume of pure water, The active ingredient, such as sulfuric acid or potassium hydroxide, is heavier than water. Because the active ingredient is heavier than water, the more active the ingredient in the electrolyte, the heavier the electrolyte will be; the heavier the electrolyte, the higher the specific gravity.

A hydrometer is a glass syringe with a float inside it. The float is in a hollow, glass tube, weighted at one end and sealed at both ends, with a scale calibrated in specific gravity marked on the side. The electrolyte to be tested is drawn into the hydrometer by the suction bulb. Enough electrolyte should be drawn into the hydrometer so that the float will rise. Hydrometers should not be filled to the extent that the float rises into the suction bulb. Since the weight of the float is at its base, the float will rise to a point determined by the weight of the electrolyte. If the electrolyte contains a large concentration of the active ingredient, the float will rise higher than if the electrolyte has a small concentration of the active ingredient.

To read the hydrometer, hold it in a vertical position and take the reading at the level of the electrolyte. Refer to the manufacturer's technical manual for battery specifications to find the correct specific gravity ranges. An example of what your manual may say about the specific gravity is that for a fully charged battery the specific gravity should be 1.280 ± 0.005. The manual may tell you to recharge the battery if the specific gravity is less than 1.250.

Always return the electrolyte in the hydrometer to the cell of the battery from which it was taken.

NOTE: Hydrometers should be flushed with fresh water after each use to prevent inaccurate readings. Storage battery hydrometers must not be used for any other purpose.

Perhaps it should be said that adding the active ingredient (sulfuric acid, for example) to the electrolyte of a discharged battery does not recharge the battery. Adding the active ingredient only increases the specific gravity of the electrolyte and does not convert the plates back to active material, and so does not bring the battery back to a charged condition. A charging current must be passed through the battery to recharge it.

Oil You must check the engine crankcase oil level before operating the generator set. The engine dipstick is the crankcase oil level gauge. The dipstick in the generator engine is the shielded type, which allows checking the oil level while the engine is either stopped or running. The dipstick is stamped on both sides to indicate the two different oil levels. The engine running side is stamped as follows: "ADD," "FULL," and "RUNNING." The engine stopped side is stamped as follows: "ADD," "FULL," and "STOPPED." Be sure to use the appropriate add and full marks, depending on whether the engine is stopped or running. Also, ensure that the appropriate side of the dipstick is up when inserting it since the underside will be wiped in the gauge tube when the dipstick is removed, therefore, indicating a false oil level reading.

To check the oil level, first remove and wipe the oil from the dipstick. Loosen and remove the oil filler cap (fig.) to allow the pressure to escape. Reinsert the dipstick (with the appropriate side up) and remove it to observe the oil level. Add oil through the fill tube, as required, to obtain the "full" level on the dipstick. Be sure to use the proper grade of oil. A lubricant chart in the instruction manual furnished with each generator will show the proper grade of oil to use at the operating temperature.

Water Check that the level of coolant is within 2 inches (51 mm) of the top of the radiator.

WARNING Do not attempt to remove the radiator cap until the radiator has cooled to a point where there will be no built-up steam pressure. Failure to observe this warning could result in second-or third-degree bums.

Using an antifreeze solution tester, check that the antifreeze content is sufficient for the existing ambient temperature. Add antifreeze as required.

Whenever you fill the radiator with coolant after it has been drained, fasten a tag near the radiator cap. The tag should indicate the type of coolant and the degree of protection the coolant gives.

Regardless of the air temperature, be sure to use an antifreeze solution in the proportions recommended in the instruction manual for the generator.

Fuel The fuel tank should be filled with clean fuel oil, strained if necessary. Service the fuel tank as follows:

WARNING Always maintain constant metal-to-metal contact between the fuel tank filler neck and the spout of the fuel supply. That will prevent the possibility of sparking caused by static electricity.

Remove the fuel tank filler cap, and fill the fuel tank with the proper fuel. (Refer to the instruction manual.) Replace the filler cap and wipe up any spilled fuel.

Remove the cap from the fuel tank drain valve and open the valve. Let water and sediment drain into an approved nonflammable container. When clean fuel runs out of the tank, close the drain valve and install the cap on the valve. A day tank is one of the major components of the fuel system. It has a capacity to permit engine operation for a minimum of 5 minutes. The day tank also provides a settling point for contaminants (to prevent their entry into the engine) and supplies fuel to the engine fuel pump.

The day tank contains a dual type of float switch. The upper float operates in conjunction with the fuel solenoid valve to maintain a predetermined fuel level in the tank. The lower float initiates an engine shut-down sequence. This sequence is initiated in the event that the fuel level in the tank will permit operation of the generator set at the rated load for only 1 minute. You must drain sediment and water from the day tank as you did from the fuel tank. Remove the cap from the day tank drain valve and open the valve. (Refer to fig. 3-1, view B, for the location of the tank and its drain valve.) Drain water and sediment into a container. Close the valve when clean fuel runs out of the tank, and install the cap back on the valve.

VENTILATION

WARNING Do not operate the generator set in an enclosed area unless the exhaust gases are piped to the outside. Inhalation ofexhaust gases will result in serious injury or death.

Keep the area around an operating generator set well ventilated at all times so that the generator set will receive a maximum supply of air. Consider ventilation when you install the units inside a building. Every internal combustionengine is a HEAT engine. Although heat does the work, excess amounts of it must be removed if the engine is to function properly. This can be accomplished by setting the radiator grille of the engine near an opening in the wall and providing another opening directly opposite the unit. In this manner, cool air can be drawn in and the hot air directed in a straight line outdoors. These openings can be shielded with adjustable louvers to prevent the entrance of rain or snow. In addition, when the generator is operating in extremely cold weather, the temperature in the room can be controlled by simply closing a portion of the discharge opening. Additional doors or windows should be provided in the shelter if the plants are installed in localities where the summer temperatures exceed 80° F at any time.

EXHAUST SYSTEM

The muffler and the exhaust pipe are connected to the turbocharger exhaust elbow (fig. 34) and provide a path for engine exhaust gases to exit the generator set. The muffler reduces the noise level of the engine exhaust. The discharge opening of the muffler is covered by a hinged cap to prevent water from entering the exhaust system when the generator is not operating. Let's look at an example of an indoor installation. After bolting the generator set to the concrete pad and enclosing it in a shelter, you are about to vent the exhaust system to the outside. You lift the exhaust cap (fig. 3-4) and connect the gastight exhaust pipe to the discharge opening. You then extend the pipe through the wall (or roof) of the building in a route that includes no obstructions and a minimum number of bends. If you have arranged the pipe to slope away from the engine, condensation will not drain back into the cylinders. If the exhaust pipe has to be installed so that loops or traps are necessary, place a drain cock at the lowest point of the system. All joints must be perfectly tight; and where the exhaust pipe passes through the wall, you must take care to prevent the discharged gas from returning along the outside of the pipe back into the building. Exhaust piping inside the building must be covered with insulation capable of withstanding a temperature of 1500° F.

Figure.- Exhaust and breather system.

The crankcase breather tube is clamped to the engine breather assembly. The breather tube provides a path for engine crankcase vapors to exit the generator set. A rain shield is provided at the tube outlet to prevent rain from entering the tube when the generator is used outdoors.

GROUNDING

The generator set must be connected to a suitable ground before operation.

WARNING Electrical faults in the generator set, load lines, or load equipment can cause injury or electrocution from contact with an ungrounded generator.

The ground can be, in order of preference, an underground metallic water piping system (fig., view A), a driven metal rod (fig.), or a buried metal plate (fig.). A ground rod must have a minimum diameter of 5/ 8 inch (41 mm) if solid or 3/ 4 inch (44 mm) if pipe. The rod must be driven to a minimum depth of 8 feet (2.44 M). A ground plate must have a minimum area of 2 square feet (0.186 square meter) and, where practical, be embedded below the permanent moisture level.

The ground lead must be at least No. 6 AWG (American Wire Gauge) copper wire. The lead must be bolted or clamped to the rod, plate, or piping system. Connect the other end of the ground lead to the generator set ground terminal stud (fig.). Use the following procedure to install ground rods:

1. Install the ground cable into the slot in the ground stud and tighten the nut against the cable.
2. Connect a ground rod coupling to the rod and install the driving stud in the coupling (fig.). Make sure that the driving stud is bottomed on the ground rod.
3. Drive the ground rod into the ground until the coupling is just above the ground surface.
4. Connect additional rod sections, as required, by removing the driving stud from the coupling and installing another rod section in the coupling. Make sure the new ground rod section is bottomed on the ground rod section previously installed. Connect another coupling on the new section and again install the driving stud.

Figure - Methods of grounding generators.

Figure - Grounding procedure.

5. After the rod( s) have been driven into the ground, remove the driving stud and the top coupling. meet the requirements, they will be not less than 6 feet apart.

NOTE: The National Electrical Code(c) states that a single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less will be augmented by additional electrodes. Where multiple rod, pipe, or plate electrodes are installed to The resistance of a ground electrode is determined primarily by the earth surrounding the electrode. The diameter of the rod has only a negligible effect on the resistance of a ground. The resistance of the soil is dependent upon the moisture content. Electrodes should be long enough to penetrate a relatively permanent moisture level and should extend well below the frost line. Periodic earth resistance measurements should be made, preferably at times when the soil would be expected to have the least moisture.

You need to test the ground rod installation to be sure it meets the requirement for minimum earth resistance. The earth resistance tester may be used to perform the test. You should make this test before you connect the ground cable to the ground rod. When ground resistances are too high, they may be reduced by one of the following methods:

1. Using additional ground rods is one of the best means of reducing the resistance to ground; for example, the combined resistance of two rods properly spaced and connected in parallel should be 60 percent of the resistance of one rod; the combined resistance of three rods should be 40 percent of that of a single rod.
2. Longer rods are particularly effective where low-resistance soils are too far below the surface to be reached with the ordinary length rods. The amount of improvement from the additional length on the rods depends on the depth of the low-resistance soils. Usually, a rather sharp decrease in the resistance measurements is noticeable when the rod has been driven to a low-resistance level.
3. Treating the soil around ground rods is a reliable and effective method for reducing ground resistance and is particularly suitable for improving high-resistance ground. The treatment method is advantageous where long rods are impractical because of rock strata or other obstructions to deep driving. There are two practical ways of accomplishing this result, as shown in figure . Where space is limited, a length of tile pipe is sunk in the ground a few inches from the ground rod and tilled to within 1 foot or so of the ground level with the treatment chemical. The best treatment chemicals for all situations cannot be covered within the scope of this manual. You may work with your engineering office to determine the possible corrosive effect on the electrode. Examples of suitable noncorrosive materials are magnesium sulfate, copper sulfate, and ordinary rock salt. The least corrosive is magnesium sulfate, but rock salt is cheaper and does the job.
The second method is applicable where a circular or semicircular trench can be dug around the ground rod to hold the chemical (fig.). The chemical must be kept several inches away from coming into direct contact with the ground rod to avoid corrosion of the rod. if you wish to start the chemical action promptly, you should go ahead and flood the treatment material. The first treatment usually contains 50 to 100 pounds of material. The chemical will retain its effectiveness for 2 to 3 years. Each replenishment of the chemical extends the effectiveness for a longer period so that the necessity for future retreating becomes less and less frequent.

Figure - Methods of soil treatment for lowering of ground resistance.

4. A combination of methods may be advantageous and necessary to provide desired ground resistance. A combination of multiple rods and soil treatment is effective and has the advantages of both of these methods; multiple long rods are effective where conditions permit this type of installation.
After you are sure you have a good ground, connect the clamp and the ground cable to the top ground rod section (fig. 3-6, view B), and secure the connection by tightening the screw.

CONNECTIONS

A typical generator set is outlined in figure, showing the load cables and output load terminals.

WARNING Before attempting to connect the load cables to the load terminals of a generator set, make sure the set is not operating and there is no input to the load.

Refer to figure as you follow this procedural discussion for making load connections. 1. Open the access door and disconnect the transparent cover by loosening six quick-release fasteners. Remove the wrench clipped to the cover.
NOTE: Be sure to maintain the proper phase relationship between the cable and the load terminals; that is, A0 to L1, B0 to L2, and so forth. 2. Attach the load cables in the following order: L0, L3, L2, and L1 as specified in step 3 below.

Figure- Load cable connections.

3. Insert the load cables through the protective sleeve. Attach the cables to their respective load terminals, one cable to each terminal, by inserting the cable in the terminal slot and tightening the terminal nut with the wrench that was clipped to the transparent cover. Install the wrench on the cover and install the cover.
4. Tighten the drawstring on the protective sleeve to prevent the entry of foreign matter through the hole around the cable. You may convert the voltage at the load terminals to 120/ 208 volts or 240/ 416 volts by properly positioning the voltage change board (fig. 3-9). The board is located directly above the load terminal board.

The procedure for positioning the voltage change board for the required output voltage is as follows:

1. Disconnect the transparent cover by loosening the six quick-release fasteners.
2. Remove the 12 nuts from the board. Move the change board up or down to align the change board arrow with the required voltage arrow. Tighten the 12 nuts to secure the board.
3. Position and secure the transparent cover with the six quick-release fasteners and close the access door.

PHASE SEQUENCE INDICATORS

The phase sequence indicator is a device used to compare the phase sequence of three-phase generators or motors. Examples of its use are as follows: to

Figure - Voltage change board.

compare the phase rotation of an incoming alternator that is to be operated in parallel with an alternator already on the line or to determine the phase rotation of motors being put into use for the first time. One type of phase sequence indicator is a tiny three-phase induction motor. The three leads of the motor are labeled "A," "B," and "C," as shown in figure 3-10. The insulating hoods over the clips are of different colors: red for A, white for B, and blue for C. The rotor in the instrument can be observed through the three ports as it turns so that you can note the direction in which it rotates. The rotor can be started by means of a momentary contact switch: it, stops again when you release the switch.

You also may use a solid-state phase sequence indicator with two lights. Whichever light is on indicates the phase sequence of the voltage in the conductors that the instrument is connected to; for example, the light labeled "ABC" indicates one phase sequence, while the other light, labeled "BAC," indicates another. If you are working with three-phase conductors (all of the same color) that are installed but not labeled, you may connect the phase sequence indicator to the three conductors, turn on the power, check the phase sequence of the conductors as connected to the instrument, and turn off the power. You may then label the conductors with numbers, letters, or colored marking tape.

You also may check the phase sequence of an incoming alternator before paralleling it with an operating load-side alternator. Connections must be made so that the phase sequence of the two generators will be the same.

Figure shows the leads of two generators to be parallel. The proper procedure for ensuring phase sequence with a phase sequence indicator is as follows: Connect indicator terminals A to X1 , B to Yl , and C to Z1 , press the contact switch, and note the direction of rotation of the rotor.

Now move the A terminal to X, the B to Y, and the C to Z, and again press the switch. If the rotor turns in the same direction as before, the phase rotation is the same for the alternators, and the connection can be made X to X1 , Y to Y1 , and Z to Z1 . If the rotor turns in the opposite direction, transpose the connections of any two of the incoming alternator leads before making the connection. It is not absolutely necessary that A be connected to the left-hand terminal, B to the center terminal, and C to the right-hand terminal. This is a practical method, however, used to avoid the danger of confusing the leads. The important thing is to ensure that the phase sequence indicator that was used on X1 be brought down to X, the one used on Y1 to Y, and the one used on Z1 to Z. Reversing any two of the leads will reverse the direction of rotation of the rotor of the instrument.

Reference :
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