Generator Protection - 1

           Generator is very essential part of power system. After all it is main element which can produce power. Any abnormal condition lead to serious damage to generator so to protect generator from various abnormal condition various protection is provided. 

15MW Generator Rewinding Process

            In this post, I am going explain various protection which is provide for generator in power plant for reliable power supply.

Sr No.	Protection Function	ANSI Code
1	Differential Protection	87G
2	Overcurrent Protection	51
3	Stator Earth fault Protection	64G
4	Standby Earth fault Protection	51N
5	Restricted Earth fault Protection	64REF
6	Negative sequence Protection	46
7	Thermal Overload	49
8	Field failure Protection	40
9	Low forward Power	32P
10	Reverse Power protection	32P
11	V/f Protection	24G
12	Inadvertent Energization	51 O/C
13	Under impedance	21
14	Voltage Controlled Overcurrent	51V
15	Out of Step	78
16	Interturn Protection	87IT
17	Under voltage	27
18	Over voltage	59
19	Residual Overvoltage	59G
20	Under frequency	81
21	Over frequency	81
22	Rate of change of frequency	81R
23	Rotor earth fault Protection	64R

              Each protection has its own principle to operate, even some protection has specific zone for operation like Differential Protection. 

         Generator current and voltage is step down to 1A/5A and 110V by Current transformer and Potential transformer respectively and feed to relays. 

            When numerical relay was not discovered each protection has separate electromechanical relay so generator protection panel was very big and complicated but nowadays only one multifunctional IED (Intelligent electronic device) also called Numerical relay is enough to provide this all protection with accuracy and precision better than electromechanical relays.

            Apart from this protections some hard wired tripping is also provided through numerical relay like turbine trip, AVR trip etc.

         I have listed some manufacturer. Listed model no.is widely used in power plant as well as industries.

Manufacturer	Model No.
SIEMENS	7UM60
AREVA, SCHNEIDER ELECTRIC	P343
ABB	REM 545
L & T	MG-30

Generator Protection P343 in Service

               You can see above image, it is numerical relay which is used to protect generator. In this relay we can configure different protections to different LEDs. When fault came, configured LED glow so operator get idea which fault came.