Thermal Overload Protection Of Generator

To understand the basic principle of thermal overload protection let s examine the schematic diagram of a basic motor control scheme.

Thermal overload protection of generator.

There is one cylindrical stator and a three phase winding is symmetrically distributed in the inner periphery of the stator. 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. Figure 2 protection schematic for generators over 5 mva. Generator protection should take into account the importance of the generator and its technical characteristics such as power voltage and earthing arrangement.

Generator thermal withstand capability from the generator manufacturer s data. 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. Schematic diagram of a basic motor control scheme. 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. A thermal overload relay works on the heat produced by the excessive overload current. The relay shall have high reset ratio and adequate continuous thermal rating. Suitable over voltage relays preferably with volt cycle characteristics shall be provided.

Generator over voltage protection 59g. Due to such symmetrical distribution when three phase power supply. One over current relay shall be provided to initiate an overload alarm. Protection against overload using thermal relays.

The most basic safety scheme of the motor is thermal with load protection which mainly covers the protection of all the above conditions. No one would do that of course because you d sacrifice much of the full generator capacity. The heat produced by the overload current is utilized to trip the motor circuit. These are mostly used for protection of low voltage squirrel cage induction motors or dc motors of lower output rating.