Marathon MX Series Generator Paralleling Operation And Troubleshooting

VII. Paralleling operation (wiring refer to the appendix):

MX generators are suitable for paralleling as full damping winding. But, before paralleling, each unit of generator should be started up, operated and adjusted.

A. Base conditions of paralleling operations:

1 . Additional paralleling circuitry

a. Voltage regulator-paralleling provisions

b. Paralleling current transformer(s)

c. Paralleling provisions on governor controls

d. Switchgear

2. The voltage and frequency must be the same for all sets with voltages in phase.

3. The generators must have the same phase sequence rotation.

4. The voltage regulation characteristics of the individual generators should be similar.

5. The driving engines should have the same speed regulation characteristics and the governors should be adjusted to give the same speed regulation.

B: Reactive load control and adjustment:

When two identical generators are operating together in parallel and an unbalance occurs in field excitation, circulating currents begin to flow between the generators. This current will appear as a lagging power factor or inductive load to the highly excited generator, and as a leading power factor or capacitive load to the generator with the lower field current. This is known as the reactive circulating current, and there are two controlling methods in parallel operation:

1. Reactive droop compensation (formerly known as parallel droop compensation) - the bus voltage droops or decreases as the reactive lagging power factor load is increased. Then the output current and power of generator decreases, thus reactive power tends to balance.

2. Reactive differential compensation (formerly known as cross current compensation) - the reactive differential compensation circuit allows parallel generators to share reactive loads with no decrease or no droop in generator voltage, The circuit must meet the following criteria:

a. All secondary circuit of current transformers for generators being paralleled must be included into interconnection loop.

b. When different size generators are paralleled, all paralleling current transformers must have the same or proportional ratios that give approximately the same secondary current.

c. Reactive differential compensation cannot be used when paralleling with the utility power. There is no limit, however, in the number of generators that can be included in this type of circuit.

The paralleling with the utility power has different wiring circuitry, means and program, consult with manufacturer if need assistance.

VIII. Thyristor or SCR Loading

Solid state electronic control devices which utilize thyristors or SCR firing circuits (such as variable frequency induction motor controls, precision motor speed controls, no-break powered battery chargers, etc.) can introduce high frequency harmonics which adversely affect or destroy the normal waveform of the generator. This creates additional heat in the generator stator and rotor and can cause overheating.

These devices can and do present problems to non-utility power generating equipment or any limited power bus system. The problems which can occur are not limited to the generator itself, but can effect the solid state control device, the equipment it controls, other associated loads, monitoring devices, or a number of combinations over the entire system.

MAGNAMAXDVR generators can supply power to thyristor or SCR loads when properly applied. When SCR loads are more than 25% of the total load, select the generator based on the 800C R/R rating. The standard voltage regulator is PMG powered and senses 3 phase RMS voltages for maximum stability against severely distorted wave forms. SCR type applications such as cranes, shovels, etc., require special consideration of the generator insulation system due to greater dielectric stress and severe environmental conditions. Please contact to Marathon Electric for application assistance.

Ⅸ.Troubleshooting