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rithinram
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Join Date: Oct 2012
Posts: 1

Low Forward Power Protection

10/27/2012 4:17 AM

Why are we using low forward power protection relays for Turbo generators?
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Joshi
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Join Date: Oct 2007
Location: India
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#1

Re: LOW FORWARD POWER PROTECTION

10/27/2012 7:30 AM

Do your homework.
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electricalexpert65
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Join Date: Oct 2009
Posts: 2061
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#2

Re: Low Forward Power Protection

10/27/2012 11:22 AM

Imagine your captive generator is in sync with the grid. The EHV side breaker of your transformer has tripped due to some fault. Now, you would not want to feed the excitation power of the HV/EHV Power Transformer. To avoid this situation, a low forward power relay is used.
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pcchatur
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Join Date: Mar 2010
Location: BHOPAL, INDIA
Posts: 201
Good Answers: 20
#3

Re: Low Forward Power Protection

10/29/2012 4:16 AM

Turbo generators are run by steam turbines. In case of turbine trip, if the generator remains connected to the grid, the generator will run as motor and rotate the turbine. With no steam in turbine, there will be air in the turbine casing. Turbine blades, specially low pressure turbine blades will offer heave windage loss thereby increasing the temperature of blades to very high value which will damage the turbine. When turbine is run by steam, temperature is limited to that of the steam. But when steam is not there, temperature will go dangerously high. So forward power relay is used to trip the generator thereby preventing the motor operation of the set. This saves the turbine from high temperature. Some utilities prefer reverse power relay over forward relay.
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electricalexpert65
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#4
In reply to #3

Re: Low Forward Power Protection

10/29/2012 9:23 AM

But this is called reverse power protection and NOT low forward power protection.
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pcchatur
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Join Date: Mar 2010
Location: BHOPAL, INDIA
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#5
In reply to #4

Re: Low Forward Power Protection

10/29/2012 9:41 AM

The purpose of both, reverse power and low forward power relays is same namely, to prevent damage to the steam turbine. In low forward power protection relay trips the generator circuit breaker when the power delivered to the grid drops below a certain level (typical setting being 0.5 % of full load). In reverse power protection relay operates immediately after the generator starts drawing power from the grid instead of delivering power to the grid. Both the philosophies are followed.
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