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

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 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

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Why Turbines go into over speed trips???

10-Difference between fixed nozzle and Variable nozzle de-super heating

  

 De-superheating is the process of reducing the temperature of superheated steam. This is typically achieved by injecting a cooling medium, such as water, into the steam flow. The nozzles used in the desuperheating process can be classified as either variable nozzle or fixed nozzle de-superheaters. Here's

 The differences between these two types are:

Sl No.	Variable nozzle de-super heater	Fixed nozzle de-super heater
1	Variable nozzle desuperheating systems have adjustable nozzles that allow for controlling the flow rate of the cooling medium injected into the steam flow.	Fixed nozzle desuperheating systems have non-adjustable nozzles, meaning the cooling water flow rate and the degree of desuperheating are fixed
2	The nozzle opening can be adjusted to vary the amount of cooling water injected, thereby controlling the degree of desuperheating and achieving the desired steam temperature.	Separate control valve is required to adjust the water flow
3	More flexibility in adjusting the cooling water flow rate and achieving precise temperature control.	Not much accuracy in temperature control
4	Variable nozzle desuperheating systems are often used in applications that require tight temperature control,	USed where there is much tolerance in temperature control, Ex: In process industries They are commonly used in applications where a constant degree of desuperheating is sufficient, such as in industrial processes with steady steam loads or in small-scale power plants.
5	Complex design	Simple design
6	More costlier than fixed nozzle de-super heaters	Less costlier
7	Little bit complicated operation	Simple operation
8	Can be used for variable inlet flow & temperature	Used only for fixed flow & temperature
9	Size of nozzle is variable	Size of nozzle is fixed
10	Maintenance is difficult & costlier	Maintenance is simple & cheaper

 The choice between a variable nozzle and fixed nozzle desuperheater depends on factors such as the required temperature control accuracy, steam flow variability, plant operating conditions, and budget considerations. Variable nozzle desuperheaters are often preferred in applications where precise temperature control and flexibility are crucial, while fixed nozzle desuperheaters can be suitable for applications with relatively stable operating conditions and lower cost requirements.

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11-differences between star connection and delta connections

 

11-differences between start connection and delta connections

Sl No.	Star connection	Delta connection
1	Two types of star connections are possible A-4-wire, 3-phase system B-3 wire. 3-phase system	Only 3 wire. 3-phase system is possible
2	Out of 4 wires, 3 wires are the phases and one is neutral	All 3 wires are phases in Delta connection
3	In Star  connection, one end of all the three wires are connected to a common point in the shape of Y to form neutral	In Delta connection every wire is connected to two adjacent wires in the form of triangle.And all the three common points of the connection form the three phases
4	Line current and phase currents are same	Line current and phase current are different.Line current =√Phase current
5	Line voltage and phase voltages are different, Line voltage =√Phase voltage	Line voltage and phase voltages are same
6	Since line voltage is more than phase voltage, insulation required for each phase is less	In Delta connection line and phase voltages are same hence more insulation is required
7	Star connections are used for both transmission and distribution applications/networks	This connection is generally used for distribution networks
8	Since insulation required is less, these connections are used for longer distances	Since insulation required is more, these connections are used for shorter distances
9	Star  connections are used where less starting current and starting torque is required	Delta connections are used where starting current and Torque is more
10	Power calculation in Start connections.   P = 3 X Vp X Ip X Cosθ   Or   P = (√3 X VL) X IL X Cosθ	Power calculation in Delta connections.   P = 3 X Vp X Ip X Cosθ   Or   P = (√3 X IL) X VL X Cosθ
11	In star connections different voltage levels are used as line voltage & phase voltages are different	In Delta connections, only single voltage is used

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