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How do you calculate setting for over current earth fault relay setting?
Wiki User
∙ 9y ago
An artificial neutral is crated in the CT of the line to be protected (for transmission lines) a CT is fixed in the neutral of the CT. if there is any imbalance in the 3 phase current then the relay will develop a difference in neutral.that can be sensed by the CT,then gives the trip command to relay
Wiki User
∙ 11y ago
Wiki User
∙ 9y agoOvercurrent and earth-fault are two different types of setting for a circuit-breaker.
Overcurrent provides the safety features of a fuse and the setting is normally equal to the ampacity of the supply circuit supplying the breaker.
Earth-fault circuit breakers disconnect the supply when any current flows in the earth wire. A normal setting is 0.015 to 0.035 amps.
The current limit is low because a current in the earth indicates that the currents in the live and neutral are unbalanced, which is a possible indication that someone is receiving an electric shock somewhere down the line from the circuit breaker.
Wiki User
∙ 11y ago1.Phase and neutral over current protection
2.Three phase high set and low set phase over current protection.
Wiki User
∙ 11y agoyes
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How do you calculate 3 phase earth fault loop?
You can't have a three phase earth fault, you can have a phase to phase or a phase to earth fault. If you want the potential phase to earth fault current it will be your voltage times your impedance. If you want the phase to phase potential fault current then you should just double the above result.
How do you calculate internal fault loop impedance?
by calculating the loop current
What is earth fault loop impedance?
An earth-fault loop is the path taken by the fault current, when an earth-fault occurs within an electrical installation, and comprises a series circuit made up ofthe utility company tranformer's low-voltage winding,the utility company's distribution cable's line conductor,the consumer's line conductor to the point of an earth fault,the consumer's earthing conductor,and the resistance of the earth path back to the transformer.The combined opposition of this series circuit to the flow of fault current is termed the earth-fault loop impedance, expressed in ohms.
Why ngt or ngr used in transformer?
Criteria-in order to protect the stator core from damage during internal earth fault it is necessary to limit the stator earth fault current al low as possible.may be upto 10amp for generator. Basis for selection of ngtr- if generator is connected to the system through generator transformer then generator can be treated as an isolated system which is not influenced by the distribution earthing system. In this case you can select earth fault current as low as possible, but if we use ngr then in order to limit the low earth fault current size of the ngr will be increased.due to big size of ngr we required more space & also its too costly. V = ir means if v constant i is inversely proportional to r exp:-to limit 10amp current , v =11kv/root 3 r = 11/root 3/10*1000=635.10 ohm ( very high value) for overcome on this, general practice to use a ngtr so that we can limit low earth current without any extra cost. Exp:- ngtr 11/240v to limit 10amp current current reflect on secondary side of ngtr will be = (11000/root 3/240)*10=264.6 amp. Resistor value on secondary side r =240/264.6 =0.9 ohm ( approximately) which is much lower than 635.10 ohm. Basis for selection of ngr- if generator is directly connected to the system then we can not limit the earth fault current up to 10 amp. We have to select the earth fault current value above the residual capacitive charging current of system.also we need to check the possibility of relay setting operation with ct ratio. For exmp- if ct ratio is 2000/1amp & earth fault limit current is 100amp relay selected with 10 % setting. Then that relay will see only 200amp earth fault current it will not see 100amp current. Also we can not keep generator solidly grounded because of high earth fault current stator can damage same will happen with ht motor if it is connected to this system. So for this case we need to select the ngr with proper earth fault current
What is the reason for using a neutral current transformer on a transformer?
A current transformer is primarily used at the neutral point of a transformer for earth fault protection. A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply of electricity to the transformer.
How do you calculate earth fault current value by knowing the setting in electromagnetic relay?
trh
How do you calculate maximum earth fault current?
transformer max earth fault current
How do you calculate 3 phase earth fault loop?
You can't have a three phase earth fault, you can have a phase to phase or a phase to earth fault. If you want the potential phase to earth fault current it will be your voltage times your impedance. If you want the phase to phase potential fault current then you should just double the above result.
What is an earth fault relay?
An earth fault relay is a relay that is activated by a fault current that flows from the power line to the earth. Earth fault relays are found in power distribution systems.
Earth fault relay and an overcurrent relay Methods to energise an earth fault relay?
Earth fault relay and an over current relay Methods to energies an earth fault relay with simulation diagram?
How do you calculate internal fault loop impedance?
by calculating the loop current
What is plug setting multiplier of relay?
the actual r.m.s current flowing in the relay expressed as a multiple of the setting current (pick up current) is known as plug setting multiplier.mathematically ,PSM= SECONDARY CURRENT/RELAY CURRENT SETTINGorPSM= (primary current during fault)/(relay current setting *C.T ratio)
What is a difference between ground fault and earth fault?
They mean the same thing, a current to ground/earth that shouldn't exist in the circuit.
Can earth fault current go up passing through the downstream panel and directly cause a trip at the upstream panel which have higher set point of earth fault protection?
If the fault is a direct short to ground, the fault current can be high enough to trip the upstream protection.
What is the determining factor in setting the current rating of distribution equipment?
Temperature rise and fault levels.
What is earth fault loop impedance?
An earth-fault loop is the path taken by the fault current, when an earth-fault occurs within an electrical installation, and comprises a series circuit made up ofthe utility company tranformer's low-voltage winding,the utility company's distribution cable's line conductor,the consumer's line conductor to the point of an earth fault,the consumer's earthing conductor,and the resistance of the earth path back to the transformer.The combined opposition of this series circuit to the flow of fault current is termed the earth-fault loop impedance, expressed in ohms.
Why ngt or ngr used in transformer?
Criteria-in order to protect the stator core from damage during internal earth fault it is necessary to limit the stator earth fault current al low as possible.may be upto 10amp for generator. Basis for selection of ngtr- if generator is connected to the system through generator transformer then generator can be treated as an isolated system which is not influenced by the distribution earthing system. In this case you can select earth fault current as low as possible, but if we use ngr then in order to limit the low earth fault current size of the ngr will be increased.due to big size of ngr we required more space & also its too costly. V = ir means if v constant i is inversely proportional to r exp:-to limit 10amp current , v =11kv/root 3 r = 11/root 3/10*1000=635.10 ohm ( very high value) for overcome on this, general practice to use a ngtr so that we can limit low earth current without any extra cost. Exp:- ngtr 11/240v to limit 10amp current current reflect on secondary side of ngtr will be = (11000/root 3/240)*10=264.6 amp. Resistor value on secondary side r =240/264.6 =0.9 ohm ( approximately) which is much lower than 635.10 ohm. Basis for selection of ngr- if generator is directly connected to the system then we can not limit the earth fault current up to 10 amp. We have to select the earth fault current value above the residual capacitive charging current of system.also we need to check the possibility of relay setting operation with ct ratio. For exmp- if ct ratio is 2000/1amp & earth fault limit current is 100amp relay selected with 10 % setting. Then that relay will see only 200amp earth fault current it will not see 100amp current. Also we can not keep generator solidly grounded because of high earth fault current stator can damage same will happen with ht motor if it is connected to this system. So for this case we need to select the ngr with proper earth fault current
