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What size overcurrent protection device is required to protect the secondary of a three phase 75kva and 208 v transformer supplying a 150 amp continuous load?
Wiki User
∙ 12y ago
If you're asking about load sizing, I think you already have the answer (at least 150A, although you could go up to 208 for full load, and maybe higher if you can overload the transformer). If you're talking about short circuit rating, you have entirely the wrong information. Short circuit rating will tell you if the fuse (if you're using fusing) mounting is rated to interrupt the available fault current.
Wiki User
∙ 12y ago
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How does the standby earth fault scheme work?
Restricted earth fault protection is used to protect a specific zone, and should not trip for a fault outside of that zone (usually limited to a transformer, and possibly extending to lowside, highside, and tertiary breakers). Stand by earth fault protection is a term I am not very familiar with, but I believe this would be protection that is meant for a specific zone as backup, and can operate for faults outside of this zone. An example might be a highside time overcurrent relay set looking into a transformer, where the transformer is protected by a differential (primary protection), and there is a lowside feeder with relays (primary protection). The highside overcurrent acts as a backup (secondary protection) for the transformer and the feeder, and is delayed due to the nature of a time overcurrent relay.
What is the secondary rating of a 50KVA transformer?
The secondary current is determined by the load, not by the transformer. For example, if the secondary voltage is 50 V and the load is 100 ohms, then the secondary current will be 0.5 A. If the load is 25 ohms, then the secondary current will be 2 A. It is important that a continuous secondary current doesn't exceed the rated secondary current of the transformer.
What is differential transformer protection?
The current input (primary) to a transformer is proportional to the output (secondary) current. Differential protection relays monitor these via current transformers (CT). The percentage of difference between primary and secondary can be adjusted. If it is over the seting the relay will trip the primaryand secondary feeder breakers. Thus indicating an inbalance between internal phasewindings and or shorts to earth.
Why transformer does not rotate when its secondary is connected to bearing?
How do you connect the transformer's secondary to the bearings.
Is possible to put 3 phase transformer primary as secondary and secondary as primary?
A: The only way can be possible if the transformer is an isolation type. Yes, you can put the input into the secondary side. This will create a step-up transformer.
How does the standby earth fault scheme work?
Restricted earth fault protection is used to protect a specific zone, and should not trip for a fault outside of that zone (usually limited to a transformer, and possibly extending to lowside, highside, and tertiary breakers). Stand by earth fault protection is a term I am not very familiar with, but I believe this would be protection that is meant for a specific zone as backup, and can operate for faults outside of this zone. An example might be a highside time overcurrent relay set looking into a transformer, where the transformer is protected by a differential (primary protection), and there is a lowside feeder with relays (primary protection). The highside overcurrent acts as a backup (secondary protection) for the transformer and the feeder, and is delayed due to the nature of a time overcurrent relay.
What is the secondary rating of a 50KVA transformer?
The secondary current is determined by the load, not by the transformer. For example, if the secondary voltage is 50 V and the load is 100 ohms, then the secondary current will be 0.5 A. If the load is 25 ohms, then the secondary current will be 2 A. It is important that a continuous secondary current doesn't exceed the rated secondary current of the transformer.
What is differential transformer protection?
The current input (primary) to a transformer is proportional to the output (secondary) current. Differential protection relays monitor these via current transformers (CT). The percentage of difference between primary and secondary can be adjusted. If it is over the seting the relay will trip the primaryand secondary feeder breakers. Thus indicating an inbalance between internal phasewindings and or shorts to earth.
How do you claculate the secondary load of a step up transformer?
Any continuous load shouldn't exceed the rated capacity of the transformer, expressed in volt amperes.
Does the secondary feeder of a transformer need to be rated at less than the main breaker of the feeder supply panel?
It depends on the situation and how you are utilizing the transformer. Under certain conditions the secondary does not need to be protected. The protection on the primary is enough to protect the secondary side of the transformer.
Why does the primary side of a step down transformer burn out and not the secondary of a 480V to 240V transformer?
Sounds like the wrong size fuse protection was used. The transformer should be protected to its kva capacity.
Why transformer does not rotate when its secondary is connected to bearing?
How do you connect the transformer's secondary to the bearings.
Why does a transformer need continuous rise and fall of current to induce a current into the secondary windings?
That is how inductance works. The rise is needed to charge the primary. When the field collapses, that is when the current is induced in the secondary winding(s).
How relay used for protection purpose?
Relay are operated by small current /voltage connected to Secondary side of Current Transformer and /or Voltage Transformer. The signal stimulates the magnetic substance nearby with the attracting force. This closes or opens the circuit being used in protection purpose.
When would you use current transformer?
A 'current transformer' (CT) is classified as an instrument transformer, which means it is used to provide a small secondary current that is in proportion to its large primary current, for purposes of metering or protection. At the same time, it electrically-isolates the secondary (metering) circuits from the primary circuits (which are often high-voltage circuits) for the purpose of safety.
Is possible to put 3 phase transformer primary as secondary and secondary as primary?
A: The only way can be possible if the transformer is an isolation type. Yes, you can put the input into the secondary side. This will create a step-up transformer.
How current transfomer is step up voltage transformer n step down current transformer?
Current transformers are not voltage transformers. Current transformer are used for metering or protection purposes, with single turn primary. Generally the secondary current is either 1Amps or 5Amps.
