G3516 Power Module Caterpillar

Initial Start-Up

Preparing a generator for parallel operation requires special attention. Before you attempt to parallel units for the first time, check all the units for the following three conditions:

• Same phase rotation

• Same alternating current frequency

• Same voltage adjustment

1. Check the phase rotation.

   The paralleled units must have the same phase rotation. There are two methods that are used to determine if the paralleled units have the same phase rotation. These methods are listed below:

   • Use a phase rotation meter to check the phase rotation.

   • Use a set of three light bulbs to check the phase rotation.

   The method for determining the phase rotation with three light bulbs is described below.

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   Illustration 1	g00695380

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   When servicing or repairing electric power generation equipment: Make sure the unit is off-line (disconnected from utility and/or other generators power service), and either locked out or tagged DO NOT OPERATE. Remove all fuses.

   1. Connect the light bulbs with rated voltage between the generator leads and the corresponding line phase. For example, connect terminal 1 to line 1 across the open circuit breaker.

   2. Start the units and bring the units up to speed. As the units approach the same speed, the lights will start to blink:
      • If the lights blink in sequence, one of the units is connected backward. In order to correct the problem, stop the units. Remove generator leads 1 and 3 at the circuit breaker. Exchange these generator leads. This exchange reverses the direction of phase rotation. Terminal 2 should always be connected to line 2.

      • If the lights blink in unison, the generators have the same phase rotation. The first condition of the Initial Start-Up has been met.

2. Adjust the frequency.

   The paralleled unit must operate at the same speed. Speed is proportional to the alternating current frequency.

   1. Allow each electric set to run under load for about 30 minutes.

   2. Adjust the governor control so that the unit provides the rated frequency at full load.

   3. Remove the load and check the high idle speed. The high idle speed should be approximately 2 to 5 percent above full load speed for governors that are equipped with droop. If these speeds cannot be obtained, contact your Caterpillar dealer.

   4. For the most consistent results, repeat 2.b and 2.c until the second condition of the Initial Start-Up has been met.

3. Adjust the voltage.

   There are two different methods for reactive power equalization:

   • Reactive droop compensation (Individual compensation)

   • Cross current compensation (Differential compensation)

   With reactive droop compensation, the voltage regulator causes an individual generator output voltage to change in proportion to the reactive current. The reactive current is measured with a current transformer (CT).

   The reactive current can be either lagging or leading. As the lagging reactive current flow increases, the voltage regulator will cause the generator output voltage to droop (lower) proportionally. As the leading reactive current increases, the voltage regulator will cause the generator output voltage to rise proportionally.

   This method will tend to reduce the reactive current. This method also provides better sharing of KVAR with other units. The reactive droop compensation is a standard method on the Cat generator sets. The procedure that is provided below for adjusting the voltage is for use with reactive droop compensation.

   With cross current compensation, the voltage regulator is forward biased by the difference in the reactive current outputs of the generators. Cross current compensation is similar to the reactive droop compensation. With cross current compensation, the secondary circuits of the current transformers are interconnected in a series string.

   A net difference voltage signal offsets the voltage that is generated when one of the following situations occur:

   • One of the generators carries more reactive current than the other generators.

   • There is a lagging current from one of the generators.

   • There is a leading current from one of the generators.

   The above situations will also reduce the reactive current. Refer to the Engine Data Sheet, LEKX8142, "Caterpillar Zero Droop Voltage for Parallel Operation" for the adjustment procedure.

   Note: The adjustment for the voltage level and the adjustment for the voltage droop will determine the amount of circulating currents between the generators. The circulating currents between the generators will be reduced when the voltage adjustments are carefully matched. Use the same voltmeter to make adjustments on each unit which will be paralleled.

   Note: A Voltage droop is expressed as the percentage of voltage change from no load to full load. Loads that have a power factor of 0.8 (motors) require a voltage droop on the generator of about 5 percent. Adjustments to the voltage droop that causes 3 percent to 8 percent droop in voltage is required for a satisfactory division of ampere loading.

   1. Adjust the voltage. Refer to the "Initial Start-Up" in the Operation Section, "Single Unit Operation".

   2. While the engine is running at rated speed, turn the voltage droop potentiometer clockwise about 1/2 of full range:
      • If the driven load has the unity power factor, set the voltage droop potentiometer on all of the generators at half of full range. Proceed to 3.g.

      • If the driven load has a power factor of approximately 0.8, proceed to 3.c.

   3. Readjust the voltage level rheostat until the voltage is approximately 5 percent above desired voltage.

   4. Apply full load.

   5. Readjust the voltage droop rheostat in order to obtain desired voltage with full load at 0.8 power factor. Each generator must have the same voltage droop in order to divide the reactive load.

   6. Repeat 3.c, 3.d and 3.e for each generator until the following two conditions are met:
      • The line voltage is equal to the desired level at full load.

      • The no-load voltage is approximately 5 percent above the rated voltage.

   7. Parallel the generators and apply the driven load. Check the output current of the generator. Adjust the voltage droop rheostat if the sum of the amperes of the individual generators exceeds the total amperes that are going to the load by 10 percent at full load. This adjustment will lead to proportional current sharing between generators. Some circulating current is permitted at light load. Some circulating current can be expected when generators are cold.

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   NOTICE
   Damage to the generator is possible. Do NOT exceed the rated ampere load on any single generator.

   8. Make final adjustments after the generators have been running at full load for 1 hour or more. Tighten the locknuts on all controls. Install the access cover. The last condition of the Initial Start-Up has been met.

Starting Multiple Units

Start multiple units in the same way as single units. Refer to Operation Section, "Single Unit Operation".

Paralleling Multiple Units

Units may be connected in parallel at no load or with units under load. After meeting the conditions for the initial start-up, check for the following requirements:

• One of the governors can be an isochronous governor. Electronic load sharing governors are an exception.

• Generators must have voltage droop compensation or cross current compensation.

1. Start the unit which will be paralleled.

2. Turn on the synchronizer lights.

3. After the engine has run a few minutes, bring the engine up to synchronous speed. Synchronous speed occurs when the two units are at the same frequency. The synchronizing lights will begin to blink.

   Note: The frequency of the incoming unit should be slightly greater than the line frequency. This situation allows the incoming unit to take on some of the load instead of adding to the system load.

4. Use the governor control to adjust the engine speed until the lights blink slowly.

5. The lights will turn off when the voltages of the units are concurrent. Quickly close the breaker while the lights are out.

6. Use governor controls in order to share kW load between engines.

7. Generator temperature will be stabilized in approximately 1 hour. After the temperature of the generator has been stabilized, adjust the voltage droop rheostat of each generator so that the generators share the reactive load. This adjustment will also help to limit the circulating currents. Less droop increases the reactive current that is carried by the generator. Adjust the voltage droop rheostat in a counterclockwise direction in order to decrease the droop. Adjust the voltage droop rheostat in a clockwise direction to increase the droop.

Load Division / Speed Droop (If Equipped)

Once the two units have been connected in parallel, the sharing of the kW load is determined by the governor control setting. If two units of the same capacity and the same governor characteristics have the same governor control settings, the units will share the load equally. The total load must not exceed the capacity of the one engine.

Use the following procedure in order to transfer the load from one engine to another engine.

1. Increase the governor speed control of one unit in order to increase the load.

2. Reduce the governor speed control of the other unit in order to decrease the load on that unit.

3. Raise or lower the governor speed control of both units in order to change system frequency.

Parallel Operation Of Governors

The governor that is used on 3500B power modules is shown below.

Illustration 2	g00630841
Load Sharing Module (typical example)

The load sharing module can provide either droop load sharing for generators in parallel applications, or the isochronous load sharing for generators in parallel applications. The load sharing module has an input for the synchronizing parallel module ("SPM-A"). The module provides proportional load sharing. More information is available in the System Operation, Testing and Adjusting, SENR6565, "Generator Set Load Sensor and Generator Load Sharing Module".

The speed brick converter changes the analog signal of the speed potentiometer (SP) into a pulse width modulated signal. This signal can be recognized by the engine electronic control. The converter is mounted on the subpanel which is located within the control panel.

Function of The Engine Governor

This section describes the function of the engine governor in relation to load division between parallel electric sets. For detailed information on governor controls and adjustments, refer to the Service Manual for additional information.

There are two basic facts about load division between generator sets which are operating in parallel.

1. The power that is supplied to the generator and to the load is a function of the engine. The engine governor settings and the positions of the governor controls determine the amount of power that is delivered by the engine. Therefore, the engine governor settings and the positions of the governor controls determine the kW load which is carried by the generator. If the governor control setting is advanced, the engine and the generator will assume more kW load. At the same time, other units on the line will reduce load. Likewise, decreasing the governor control setting will result in a reduction of load on the unit. At the same time, any other units on the line will gain load. These other units will assume that no change in total load or no change in the governor settings of the other units has taken place.

2. The division of power is not determined by generator excitation or terminal voltage. The power factor of a generator that is connected in parallel with other generators is determined by the excitation.

Governors that are used with Cat powered electric sets can be of two types: governors with fixed speed droop or governors with adjustable speed droop. The values of speed droop which are commonly used are 3 percent and 0 percent. Governors with adjustable speed droop can be adjusted so the characteristics closely match the characteristics of governors with fixed speed droop. When the governor is adjusted for isochronous operation, the same speed can be obtained from no load to full load.

Summary on Governor Operation

The preceding discussion of governor operation can be summarized below:

• There is a simple combination for generator sets that are connected in parallel. Set the speed droop of each governor at approximately 3 percent. If a constant frequency from no load to full load is required, one governor can be adjusted for isochronous operation. This isochronous unit will be called a "lead unit".

• The following governor adjustments are required in order for all paralleled units to share the load equally. The governors should have the same full load speed. Governors that are adjusted for speed droop operation should have the same high idle speed. Governor controls should be set to the high idle position so that the full range is available.

• The operation of an isochronous governor that is in parallel with speed droop governors requires special techniques.

• Any number of electric sets can be operated in parallel. However, only one governor of the group can be adjusted for isochronous operation. The exception will be some special cases of electronic governors with automatic load sharing.

Stopping

In order to remove a generator from the line, perform the following procedure.

1. Check the load. The load must be less than the rated capacity of the remaining units.

2. Be sure that the neutral of one of the remaining units is grounded.

3. Remove the load from the outgoing unit. Refer to the Parallel Operation, "Load Division - Speed Droop". The amperage may never go to zero due to circulating currents.

4. Open the circuit breaker.

5. Allow the engine to cool for 5 minutes.

6. Stop the engine.

Circulating Currents

Understanding the circulating currents becomes important when you parallel the units. These circulating currents flow between generators that are connected in parallel. These circulating currents are caused by voltage differences between the generators. Circulating currents do not perform useful work. The amount of the circulating current can be determined by subtracting the amperage which is going to the load from the total generator amperage.

The circulating current may be as high as 25 percent of rated amperes with cold generator sets. Such current may not even be considered harmful. The total generator current should not exceed the amperage rating.

As the generators warm, the circulating currents will decrease. The ammeter readings should decrease slightly, but the voltage meter readings should remain constant.