86 and 94 lockout relays

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bejoyengineer

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I don't understand why is it that they use an 86 lock out triping relay for the transformer protection side and 94 lockout for the distance protection side. Both have got the same functions so they could have used the same lockout i.e either the 86 or the 94 for both the distance and transformer protection.
 
bejoyengineer said:
I don't understand why is it that they use an 86 lock out triping relay for the transformer protection side and 94 lockout for the distance protection side. Both have got the same functions so they could have used the same lockout i.e either the 86 or the 94 for both the distance and transformer protection.
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You see that a lot with similar devices used in different application get assigned different device function numbers, just helps I.D. them better on a print I guess.
 
fuse failure supervision - 98

fuse failure supervision - 98

How and for what purpose does a fuse failure supervision relay work. as the name suggests - it's understood that it checks the status of the fuse but i have noticed that both the measureing and reference voltages are taken form the same primary source. . so which part of the circuit does it try protecting. any good links to get a good idea of this supervision relay. thanks in advance
 
86 versus 94

86 versus 94

Bejoyengineer- A 94 relay is a tripping relay that does not latch or require a manual reset. An 86 lockout is latching relay used for catastrophic failures. It locks out the breakers to prevent reenergizing the system. An 86 requires a manual reset (some can be reset remotely). It makes the operator think about what has happened and what he needs to check before returning power. Good 86 circuit design opens the breakers close circuit as well as energizing the trip coil.

A transformer 86 won't trip unless a major fault is detected in the transformer (differential overcurrent, sudden pressure, short circuit). You don't want to renergize until it has been checked out.

But a distance relay is monitoring a transmission line that may be equipped with reclosing. A lightning caused flashover can be cured by opening the breaker, waiting a few cycles, then reclosing the breaker to return power to the customers. If the distance relay used an 86 to trip the breakers, any reclosing would be locked out and a preventable outage might occur.

Use an 86 when you want it to stay denergized, a 94 when it may be OK to return power.

Why not just have the protective relays trip the breaker directly instead of using a 94 relay that adds a few milliseconds to the tripping time? Maybe there is more than one breaker that needs to trip. Maybe another 94 output contact intiates a breaker failure scheme or a sequential event recorder or a SCADA input. Maybe the 94 contact energizes trip coil #2 on the same breaker while the relay trips coil #1. Using the 94 relay contact keeps the two trip coil circuits seperated so a commmon failure doesn't take everything down.

You have good questions. Keep asking.
 
rcwilson said:
Bejoyengineer- A 94 relay is a tripping relay that does not latch or require a manual reset. An 86 lockout is latching relay used for catastrophic failures. It locks out the breakers to prevent reenergizing the system. An 86 requires a manual reset (some can be reset remotely). It makes the operator think about what has happened and what he needs to check before returning power. Good 86 circuit design opens the breakers close circuit as well as energizing the trip coil.

A transformer 86 won't trip unless a major fault is detected in the transformer (differential overcurrent, sudden pressure, short circuit). You don't want to renergize until it has been checked out.

But a distance relay is monitoring a transmission line that may be equipped with reclosing. A lightning caused flashover can be cured by opening the breaker, waiting a few cycles, then reclosing the breaker to return power to the customers. If the distance relay used an 86 to trip the breakers, any reclosing would be locked out and a preventable outage might occur.

Use an 86 when you want it to stay denergized, a 94 when it may be OK to return power.

Why not just have the protective relays trip the breaker directly instead of using a 94 relay that adds a few milliseconds to the tripping time? Maybe there is more than one breaker that needs to trip. Maybe another 94 output contact intiates a breaker failure scheme or a sequential event recorder or a SCADA input. Maybe the 94 contact energizes trip coil #2 on the same breaker while the relay trips coil #1. Using the 94 relay contact keeps the two trip coil circuits seperated so a commmon failure doesn't take everything down.

You have good questions. Keep asking.
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The 94 relay usually initiates circuit breaker trip, breaker reclosure, and breaker failure when the fault is considered temporary, as in an overhead transmission line. The hand-reset 86 LOR is used when the fault is considered permanent as in a differential operation, electric-reset and self-reset 86 LORs can also be used for temporary fault conditions when it is desirable to reclose the tripped circuit breakers. The 86 LOR has many more contacts than the 94 relay and therefore can trip or initiate many more operations then that of the 94 relay.
 
86 and 94 lock out relays

86 and 94 lock out relays

""""But a distance relay is monitoring a transmission line that may be equipped with reclosing. A lightning caused flashover can be cured by opening the breaker, waiting a few cycles, then reclosing the breaker to return power to the customers. If the distance relay used an 86 to trip the breakers, any reclosing would be locked out and a preventable outage might occur.""""

this made me think of another question. so now what if the fault is going to be a permenent fault on the transmission line side. will the lock out 94 keep on resetting . in the substation that i work ,i don't find a auto reclosing. so exactly does the circuit go or in another way - how does 94 actually work when a fault is permenent.
 
bejoyengineer said:
...will the lock out 94 keep on resetting . in the substation that i work ,i don't find a auto reclosing. so exactly does the circuit go or in another way - how does 94 actually work when a fault is permenent.
Click to expand...
The 94 is not a lockout relay. If there is no autoreclosing, then the circuit doesn't reclose unless the breaker is manually closed or is closed through SCADA. A lockout relay (86) would prevent manual closing by having a latched normally closed contact in the close circuit. If the 86 is tripped, and until it is reset, the 86 contact in the close circuit is open and prevents voltage from reaching the closing coil.
 
djohns6 said:
Depends on the voltage . Distribution feeders on our system might reclose 3 times . 138 kv or 230 kv circuit breakers , MAYBE once .
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The reclosure circuit exists only on overhead transmission and distribution feeders, any fault on an underground is considered a permanent fault and no reclosure is allowed. The normal reclosure for a distribution is 3 shots. The first is instantaneous, if it trips, the second usually waits 30 seconds and then recloses, if it trips again it waits an additional 60 seconds to reclose, it it trips again, it lockout and will not reclose until manually reset as the fault is considered permanent. On transmission circuits it is usually a single shot, this is to provide rapid restoration in the event of a temporary line fault, tree branch hitting the line, wind blowing the lines too close to each other, etc.

The 94 relay is a high speed (2.5 - 4.0 mS) to trip, this is much faster then an LOR which for Electroswitch is about 8.0 mS, for an HEA or WL it runs about 12-15 mS. So you can see it is designed for high speed tripping where no lockout is needed, reclosure circuit or not.
 
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