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REF, or restricted earth fault protection is normally applied to Transformers. The idea is to set a very sensitive overcurrent on the neutral of a Wye winding. For ground faults, current will flow up the neutral, triggering this overcurrent relay to operate very quickly. To prevent this relay from tripping for faults outside "the protected zone" (such as out on a line near the transformer), information is gathered from the high, low, and sometimes tertiary windings of the transformer to determine if the fault is inside the current transformers used to gather information for protecting the transformer (can be in the transformer bushings, but is often in the breakers that operate to protect the transformer) or outside them. If inside, the overcurrent is allowed to operate. If outside, the overcurrent is restrained from operating.
What else can I help you with?
How you using ref relay in transformer?
an REF relay (restricted earth fault) is used to provide ground fault protection for a transformer. Its' operation is limited by CTs starred towards the transformer (usually on the transformer bushings or in breakers used to isolate the transformer), so it will only operate for transformer related faults. Because of this, it can be set to operate very quickly.
What is restricted earth fault protection and how is it provided?
A Restricted Earth Fault (REF) means an earth fault from a restricted/localized zone of a circuit. The term "REF protection method " means not to sense any earth faults outside this restricted zone. REF is a type of "unit protection" applied to transformers or generators and is more sensitive than the method known as differential protection. An REF relay works by measuring the actual current flowing to earth from the frame of the unit. If that current exceeds a certain preset maximum value of milliAmps (mA) then the relay will trip to cut off the power supply to the unit. Differential protection can also be used to protect the windings of a transformer by comparing the current in the power supply's neutral wire with the current in the phase wire: if the currents are equal then the differential protection relay will not operate; if there is a current imbalance then the differential protection relay operates. However, REF protection is also applied to transformers in order to detect ground faults on a given winding much more sensitively than differential protection can do.
What is an Unrestricted Earth Fault?
I'm guessing this is in reference to a restricted earth fault, and you want to know what the opposite is? Restricted earth fault protection is designed to operate for earth faults within a specific zone. Unrestricted protection will operate for faults "anywhere", as long as the pickup can be satisfied. For example, REF (restricted earth fault) transformer protection looks for a small amount of neutral current, and if this exists, and the relay identifies this current as being within the zone of protection, the relay will trip. If it were unrestricted, the small amount of neutral current alone would be enough to cause a trip.
When shall you use class x CT?
in substation protection To be connected to unit protection relays (i.e. differential, REF, Dist., etc.)
Will REF protect the outgoing cables when the Ct's are fitted at the transformer?
REF protection, when installed and set correctly, will protect everything within the CT's. If the CTs are on breakers, then yes, the cables from the transformer to the breakers will be in the zone of protection. If the CTs used are in the bushings of the transformer, then no.
Calculation of restricted earth fault relay stabilizing resistor?
Requirement of REF protection for 50KVA 11KV/.4KV transforemr
What Happen if BUS BAR Protection relay fails?
In the event of a busbar fault, the next level of protection will operate and disconnect the busbars.
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What is slang for referee?
ref just ref or you could spell it reff
Does yahoo email have good spam mail protection?
Most email services offer spam protection like that are fair to middling. There are additional filters a user can operate in order to get the most of their spam mail protection.
How do you do for phase sequence protection at three phase motor operation?
motor is designed to operate in forward and reverse direction for the purpose of elevator. Phase sequence protection is not required.
How is restricted earth fault called so how is it restricted?
A Restricted Earth Fault (REF) refers to a method of fault protection that is applied to electrical system units, such as transformers or generators, that is more sensitive than the method known as Differential Protection (DP).An REF relay works by measuring the actual current flowing to earth from the frame of the unit. If that current exceeds a certain preset maximum value of milliamps (mA) then the relay will trip to cut off the power supply to the unit.REF protection is applied on transformers in order to detect ground faults on a given winding more sensitively than when only using differential protection.Differential Protection is commonly used to protect the windings of a transformer by comparing the current in the power supply's neutral wire with the current in the phase wire. If the currents are equal then the DP Relay will not operate. If there is a current imbalance then the DP Relay operates.REF and DP protection devices operate in similar ways to a GFCI or RCD device, which combines both REF and DP functions inside the one single device.For more information about GFCIs and RCDs, please see the answer to the Related Question shown below.
