Plotting undervoltage and overcurrent relays on same amps base

[brainsalad]

Greetings:

Wondering if anyone can share more examples or experiences with coordinating undervoltage and overcurrent relays. The paper

"Allowing for decrement and fault voltage in industrial relaying", Arnold Kelly
Industry and General Applications, IEEE Transactions on
Date of Publication: March 1965
Volume: IGA-1 , Issue: 2
Page(s): 130 - 139

has a nice example (picture attached) but I'd be interested in your opinions. Thanks for your thoughts.

 

[DTR2011]

Are you trying to independently coordinate 2 separate relays (27 & 51 - for motors (?)) or are you looking into generator protection such as 51/27R?

If the later, Basler has some application notes available on their website Basler 51/27R. You will have to register to download. There also appears to be a mathcad file available for download.

The intro of the paper is:

"VOLTAGE RESTRAINED TIME OVERCURRENT RELAY
PRINCIPLES, COORDINATION, AND
DYNAMIC TESTING CONSIDERATIONS
INTRODUCTION
The coordination of voltage restrained time overcurrent relays is usually based on static
characteristics in which the time-current plots assume constant current. This assumption
greatly simplifies the coordination process but fails to account for the slow-down effect due
to the decrement in generator fault currents. This paper addresses the dynamic response
of 51/27R relays in which the overcurrent element conforms to the dynamic characteristic
defined in the ANSI C37.112 standard. The purpose of this analysis is to compare the
results obtained from a proposed approximation to the exact timing results derived from a
relay model and actual test."

The reference section may also be useful.

[1] Baker, Davis S., Generator Backup Protection, IEEE Transactions on Industry
Applications, Nov/Dec 1982.
[2] Ventruella, Del, and Pete Stectuk. A Second Look at Generator 51V Relays, IEEE
Transactions.

 

[brainsalad]

smallgreek: thanks for your response. I am coordinating incoming feeder phase overcurrent relays with 4.16kV bus undervoltage (loss of voltage) relaying.

 

[mgtrp]

Are you using the undervoltage as a backup to the overcurrent relays, or just to open the circuit breaker in the event of loss-of-supply?

If the latter, I generally choose a maximum clearing time for any fault (often around 5 seconds), and set the undervoltage relay delay to something longer than this. I'm not typically concerned with momentary loss-of-supply, perhaps you are which is why you need better coordination?

 

[brainsalad]

Thanks mgtrp. The undervoltage relays are only supposed to transfer the source when there is truly a loss of voltage situation, not when there is a dip from a phase fault. So I'm in the process of coordinating these devices...

 

[brainsalad]

Attached are two pages from the paper to help clarify the problem - this shows one method of performing UV vs. OC coordination...Thanks for your thoughts.