Generator and Turbine intertripping

Case-1

 On tripping of class A trip of Generator

1-Generator breaker opens

2-Excitation switches off

3-Turbine trips on 86 T relay and followed by closing of ESV and all extractions

4-Turbine speed increases a bit by around 2-3% and gradually speed recedes

 Case-2

 On tripping of class-B trip of Generator

 1-Only generator breaker opens and excitation switches off

2-Turbine rotates on rated speed

3-After normalization of problem, generator synchronized with auxiliary power supply unit and later with grid

4-In case of small turbines, STG clubbed with 86GA to trip Turbine also

 Case-3

 On tripping due to Turbine fault

 1-Relay 86 T gets activated to close turbine ESV all extractions

2-Low forward power or Reverse Power Relay activates first which has time delay, during this time entrapped energy gets consumed by generator

3-Subsequently 86 G relay gets activated to open Generator breaker and followed by excitation gets off

4-Turbine speed does not increase in this case

 Trend of rotor speed on tripping of Turbine and Generator

Read>>>>Powerplant O&M reference books

 On tripping of Generator, instantly generator breaker gets opened and Turbine emergency valve closes.So steam entrapped in Turbine casing causes increase in speed initially and later slows down.

On the other hand,when turbine trips first, generator breaker opens after some time delay through Low forward power or Reverse Power Relay.This time delay helps turbine to consume entrapped steam in casing.As a result turbine generates power and does not allow speed to increase more.

 Relays and significance

Sl No.	Type of relay	Used for
1	86-G	Generator lock out relay
2	86-T	Turbine lock out relay
3	59-G	Generator over voltage @110% alarm and 120% trip
4	27-G	Generator under voltage @90% alarm and 80% trip
5	81-U	Generator Under frequency
6	81-O	Generator over frequency
7	32-P	Generator Reverse Active Power  5 % of Active Power
8	32Q	Generator Reverse Reactive Power
9	37	Low forward Power
10	46	Negative Phase Sequence
11	49	Generator Over Load
12	50	Generator Instantaneous O/C
13	64N	Restricted E/F
14	64R	Rotor E/F2nd Stage

Read Powerplant and calculations

Why Turbines go into over speed trips???