Generator Protection Devices have been discussed in this article and they are as follows:
● Over Current Inverse Time Relay OCIR
● Over Current Instantaneous
● Negative Phase Sequence NPS
● Current Differential
● Earth Leakage Relay
● Under And Over Frequency
● Lock Out Trip
● Reverse Power Trip
● Over or Under Voltage
So these were the safeties provided for the generator when it comes to power systems. Also apart from them temperature of windings and air are some of the added safeties. If you are interested in reading safeties for the generator engine itself, then read them. So we will read the above mentioned safeties provided in detail, one by one.
Generator Protection Devices
Let’s discuss them in detail one by one:
1) Over Current Inverse Time Relay
This protection device will continuously monitor the current values over a time. These setting are generally set during the commissioning of the generator. The time duration is generally large here. For example I is greater than .2 times more than normal load, and t is 1 to 10s.
2) Over current Instantaneous
This is similar to OCIR but the time duration is greatly reduced and the current rise is also high.
For example- I greater than 2 to 10 times more than normal load and T = .1 to 1 secs. This is kind of instantaneous trip and will be quick in action. Such scenario develops in case there is a short circuit and large current starts to follow.
3) Negative Phase Sequence Relay
It monitors the unbalance of current across the stator phase. And we know that if the temperature increases such unbalance will be more as compared to at a lower temperature. So if the current unbalance is increases slightly then indirectly temperature rise will be more. For such reason NPS setting is always kept low and around 0.2 times the normal load.
4) Current Differential
As name suggest it measures the difference in the current across different phases in the generator. Such difference can only occur if there is damage to the insulation of the windings or there is partial short circuit.
5) Earth Relay
This is kind of protection against the earth fault and will prevent the current to surge in case there is earth fault. Usually the neutral of the generator is attached to the hull with a help of a NER. You can read more about this system here.
6) Under or Over Frequency
Such safety system comes in play during paralleling or single run. If the frequency on the output is less, then it will trip the generator. Let’s say generator is running and then there is change in the load, ideally the generator is meant to maintain 60 or 50 Hz frequency. But if it drops like 55 or go over 65, then it will trip generator.
7) Lock out Trip
This is responsible for tripping the circuit breaker of the generator. This gets feeds from other generators protective devices and will trip the breaker in case there is a problem with generator.
8) Reverse Power Trip
Reverse power happens when the generator becomes a motor. It starts drawing power from the power system of the ship. In such case, one generator will keep on getting overloaded, and will eventually going to fail as the other generator which has become motor will keep on drawing power.
9) Under or Overvoltage
In case there is an over or under voltage at the output of the generator, this trip will work. Generally under voltage is required as the protection device.
So this was all from the article on the protection devices of the generator, hope you enjoyed reading them.
