Thermal Overload Protection Of Generator

Schematic diagram of a basic motor control scheme.

Thermal overload protection of generator.

One over current relay shall be provided to initiate an overload alarm. A thermal overload relay works on the heat produced by the excessive overload current. Figure 2 protection schematic for generators over 5 mva. Refer to figure 1 for graphical representation.

Generator protection should take into account the importance of the generator and its technical characteristics such as power voltage and earthing arrangement. These are mostly used for protection of low voltage squirrel cage induction motors or dc motors of lower output rating. Although over current relays negative phase sequence relays and devises for monitoring constant flow are also used to provide a certain degree of thermal overload protection. Set overload protection function so that it falls to the left of the generator thermal withstand curve.

Low vacuum protection this protection usually is in the form of a regulator which compares the vacuum against atmospheric pressure it is normally fitted to the generator set above 30 mw. Circuit breaker overload function generator thermal withstand 4. To understand the basic principle of thermal overload protection let s examine the schematic diagram of a basic motor control scheme. In general for a typical non electronic thermal magnetic circuit breaker to provide effective generator overload protection it may need to be sized as low as 50 of the generator fla.

Protection against overload using thermal relays. For understanding motor thermal overload protection in induction motor we can discuss the operating principle of three phase induction motor. No one would do that of course because you d sacrifice much of the full generator capacity. Generator over voltage protection 59g.

Suitable over voltage relays preferably with volt cycle characteristics shall be provided. Generator thermal withstand capability from the generator manufacturer s data. Due to such symmetrical distribution when three phase power supply. The relay shall have high reset ratio and adequate continuous thermal rating.