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Diesel generator set parallel operation to pay attention to the protection of the current circuit
July 13, 2022
Parallel operation of generator sets means that two or more generator sets, with equal rated voltage and consistent phase, are simultaneously integrated into the same bus to supply active power and reactive capacity to the device. 1 generator set starts up first, after which the voltage generated is sent to the bus, and after another generator set starts up, at this moment and the former 1 generator set is well parallel, should be closed at the moment, the generator set will not occur un Normal inrush current, and the crankshaft will not be impacted between suddenly, but the user should pay attention to the protection of the overall current circuit when running in parallel.
1, reverse power reverse power is the status of the generator set speed and voltage is not the same, that is, a generator set with positive power, while another unit with negative power. In other words, the unit with negative capacity becomes a load at this time (this unit has a low frequency and inconsistent speed status). When the voltage is not consistent, the unit with high voltage supplies a reactive current and reactive voltage to the unit with low voltage (the ammeter of this unit indicates positively), which is equivalent to adding a phase-shifting unit in this power supply system. The unit with low voltage becomes a large load and receives a large reactive current to ensure the voltage balance of the two units (the current meter of this unit indicates in the reverse direction). Monitoring when the voltage of one 1 unit is turned up, or the voltage size of another unit, 1 unit occurs to have a reverse power current, and its behavior current is 20% of the rated current up and down. Reverse-acting relay behavior, tripping, alarm, but not shut down.
2. Overcurrent today's generator set output capacity accordingly, its overload level is very low, most in the output capacity of 5% up and down, allowable carrying time 15 to 30 minutes, up to 60 minutes, more than this time, the generator set will be hot, the cable line insulation will be reduced, also reduces the service life. Therefore, in setting overcurrent protection without special requirements, overcurrent protection is set at 110% of the rated current. When testing with load, bring the current to 110% of the rated flow, the overcurrent relay acts. Trip, alarm, no shutdown.
3, overvoltage in parallel use of generator sets are most afraid of power supply system oscillation, but the occurrence of oscillation system voltage rise, easy to produce power facilities and power supply system insulation breakdown, so that the power supply system and power facilities a piece of the normal operation. For this reason, side-by-side generator sets are equipped with overvoltage protection, the preset value of 105% of the rated voltage is better. Shorting overvoltage relay, tripping shutdown, alarm behavior. Thus, it is important to adjust the rate (frequency) of the two units to maintain the same before preparing for the parallel operation of the generator set. And in parallel, you can adjust the speed of the first machine or the group to be paralleled according to the rotational speed rate of the same period table, so that the same period table rotates in a clockwise or counterclockwise direction, the rate is very slow the better, but the pointer of the same period table must rotate before you can parallel. Finally, after the parallel row, observe and check whether the current and capacity of the two units are balanced, if the difference is too big, adjust the rate knob to adjust the power of the two units to keep the same, so that it can be safe and reliable.
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