Generator Voltage restrained Over Current Protection

Voltage restrained Over Current Protection:

Normal IDMT Over current is not work – when a over current fault occurs, due to higher current levels, there would be a drop in terminal voltage. For the same fault impedance, the fault current will reduce (with respect to terminal voltage) to a level below the pickup setting. Consequently normal IDMT may not pick up. It is necessary to have a relay shoes pick up setting will automatically reduce in proportion to terminal voltage. Hence the over current protection must be voltage restrained. Two levels of Over current protection is required-low set and high set (for short circuit protection).

Thermal Overload:

This protection is a must – it monitors the thermal status of machine for currents between 105% to the low set 0/C level (normally 150%).

Current Unbalance:

Generators are expected to feed unbalanced loads – whose level has to be monitored. If the unbalance load exceeds 20%, it may cause over heating of the windings. This heating will not be detected by the thermal overload relay – since the phase currents will be within limits. A two level monitoring for unbalance is preferred – first level for alarm and the second level for trip.

Under / Over Voltage: Over & under voltage relay is used to protect the machine from abnormal voltage levels, particularly during synchronization and load throw of conditions.

Under / Over frequency: Over & under frequency relay is used to protect the machine from abnormal frequency levels, particularly during synchronization and load throw off conditions. This also helps in load shedding schemes for the generator.

Breaker Failure Protection: This protection detects the failure of breaker to open after receipt of trip signal. Another trip contact is generated under breaker fail conditions, with which more drastic measures (like engine stoppage, power off etc) can be taken.

Ground-Fault Relay Protection Schemes: Ground fault protection can save lives in sub-station. A Ground Fault Circuit Interrupter (GFCI) can protect against electrocution by shutting down power when it detects a lack of current. Grainger’s line of protection is perfect for industrial areas like factories or construction sites. Keep your workers safe, and your workplace up and running with these great protection products.

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