Differential protection of transformer differential relays. Pdf line current differential protection creates challenges for relay design and application. The events of transformer ultrasaturation during inrush and very low second harmonic. In this simple scheme, we can assume that under normal operating conditions, the current entering into the piece of equipment under protection is equal. Lcb ii highspeed current differential relay system. Should a fault occur inside the zone of relay protection that is between the cts, the differential relay would receive current in the operating coil. Inrush currents tend to be asymmetrical when viewed on an oscilloscope.
In current differential relay two current transformers are fitted on the either side of the equipment to be protected. Understanding and analyzing event report information. Set the differential elements with either a single or dualslope percentage differential characteristic. Learn the basics of differential protection of transformers. When no fault is present in the protected equipment, the sum of current phasors i1 and i2 is null i. The sel587 current differential relay combines overcurrent and differential elements in an easytoapply power apparatus differential protection package. Biaseddifferential protection is an older design of protection than high impedance circulating current. A currentbased solution for transformer differential. Jul 07, 2019 differential protective relay is a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents. Abstractthis paper describes an event in which lightning struck and discharged current into the phase conductor of a.
Lcb ii highspeed current differential relay system the lcb ii provides high speed protection for long and short lines it is particularly suitable for lines too short to be protected by impedance measuring systems, such as the run from generator to switchyard. Multiwinding current differential protection apply the sel387 relay for protection of two, three, or fourwinding power transformers. It is assumed with these schemes that a certain degree of ct saturation is possible under throughfault conditions. The alp series covers differential protection and accounts for current transformer errors by providing a two slope differential setting characteristic. The ratio of the current transformers are so chosen, the secondary currents of both current transformers matches each other in magnitude.
Lcb input current transformers are connected to phase currents only. The sel387a current differential and overcurrent relay has three differential elements that use operate and restraint quantities calculated from the twowinding input currents. More reliable operation than conventional systems is possible by advanced lcb features, many of which. This is especially true of line current differential applications applied to breakerandahalf and ringbus configurations. Oct 02, 2016 learn the basics of differential protection of transformers. Differential protection of a transformer the transformer is one of the major equipment in power system.
The 800168 relay is designed for use with threewinding transformers, and has three through current restraint circuits and one differential current circuit. Protective relays, associated communication systems, voltage and current sensing devices. Relay security is achieved by an optimized set of userselect. This is designed to response to the differential current in the term of its fractional relation to the current flowing through the protected section. Relay security is achieved by an optimized set of userselectable restraining and blocking elements. The sel311l relay implements line current differential protection using communications interfaces, a processor, and contact outputs separate from those used for backup protection and control.
Paralleling cts for line current differential applications. Similarly, the number and type of relay elements monitored and captured in an event report will vary by relay model. Biased differential protection is an older design of protection than high impedance circulating current. Any differential current relay will naturally see this difference as a fault, and may trip power to the transformer unnecessarily. A currentbased solution for transformer differential protection. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. A differential relay is defined as the relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined amount. Differential is generally applied for both pilot wire relays and digital current differential relays. Instruction manual sel387e relay current differential and voltage protection relay instruction manual. Each set of threephase current input terminals has phase. This function is substantially more sensitive than the differential protection during faults to ground in a winding, detecting fault currents as small as 10 % of the transformer rated current. It is a static device, totally enclosed and usually oil immersed, and therefore the fault occurs on them are usually rare. Although nowadays differential protection is achieved numerically, in order to understand the principles of differential protection it is useful to analyze the ubiquitous electromechanical relay. Participants at the time this draft was completed, the d32 working group had the following membership.
Differential relay current differential relay biased. Sel387e current differential and voltage relay protection expand transformer protection capabilities with restricted earth. It is widely applied to twowinding transformers except those connected to the lower distribution voltages. An alternative principle for line protection that is quickly becoming the norm is differential protection. Sel587 current differential relay electrical part manual s. The ratio of the current transformers are so chosen, the secondary currents of both. Pdf line current differential protection automation and. In this type of relay, there are restraining coils in addition to the operating coil of the relay. Principles of differential relaying current balance high impedance also known as unbiased differential protection only one actuating relay quantity current required for operation. A pair of identical current transformers are fitted on either end of the section to be protected alternator winding in this case. Differential current protection of transformer using arduino.
The principles of differential protection you must understand on photo. Use overcurrent elements from combined ct inputs for backup protection. Sel587 current differential relay schweitzer engineering. Jun 08, 2019 in the current differential scheme, there are two sets of current transformer each connected to either side of the equipment protected by differential relay. Product guide red615 line differential protection and control. Differential protection is applicable to all parts of the power system. Dec 06, 2017 in this video, ankit goyal cofounder at kreatryx and air 1 in gate 2014 explains how the differential relay and biased differential relay operates. Apply the sel387e current differential and voltage relay to provide comprehensive protection, metering, and automation of transformers, reactors, and other power apparatus. All protectiverelay types are derived either directly from these basic elements, by. Siprotec protection relays figure 1 shows a simple differential protection scheme, also known as a merzprice scheme. Pdf a new method for differential protection in power transformer.
This method limits the suddenpressure relay to lowcurrent incipient fault detection. Set the differential elements with either a single or dualslope percentagerestraint differential characteristic, as shown below. The differential protection relay is used for the protection of the generator, transformer, feeder, large motor, busbars etc. These elements use operate and restraint quantities calculated from the twowinding input currents. The 800168 relay is designed for use with threewinding transformers, and has three throughcurrent restraint circuits and one differential current circuit. Lcb ii current differential relay with din connectors. A new approach to current differential protection for. Pdf differential protection of power transformer in substation.
It works on the principle of comparison between the phase angle and the magnitude of the same electrical quantities. In this video, ankit goyal cofounder at kreatryx and air 1 in gate 2014 explains how the differential relay and biased differential relay operates. Selwa05010w wiring harness for sel501 and sel587 connectorized relays, features new shorting connector. Consider the comparison of the input and output current of the. Cts having the same ratio are installed in all the connections to the. Sel587 current differential relay twoterminal apparatus. The abscissa of figure 2 is given as esper thyrite disk. Line current differential protection automation and control system. The differential relay works on the principle of comparison between the phase angle.
Voltage applied hv rph 230v measured current hv ct differential core 12ma hv nct current 12ma current measured at hv ref relay terminal 0. Most of the relays discussed so far relied on excess of current for their operation. The example differential protection relay shown in the below figure is a transformer differential relay. Line current differential relay response to a direct. Sel587 current differential relay economical differential protection for power apparatus major features and benefits the sel587 current differential relay combines overcurrent and differential elements in an easytoapply power apparatus differential protection package. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected 4 the first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as overcurrent, overvoltage, reverse power flow, overfrequency, and underfrequency. Modern line current differential protection solutions hank miller and john burger, american electric power normann fischer and bogdan kasztenny, schweitzer engineering laboratories, inc. The principles of differential protection you must. Standard configurations d and e include directional. From a design perspective, the distributed nature of the. Line differential protection substation automation. Thus, the relay trip the main circuit breakers on both sides of. One line current differential relay records both local and remote phase currents in one event report.
The term current differential is generally applied for both pilot wire relays and digital current differential relays. This maloperation is caused by a spill current due to the impact of on load tap changer oltc. Pdf a currentbased solution for transformer differential. Pdf advanced line current differential protection with reduced. Sel5870, 1 connectorized current differential relay. Sep 08, 2016 observation of ref stability are as under. It improves and enhances the sensitivity of the operation of the digital differential relay that protects power transformers by discriminating between inrush current. May 15, 2018 generally differential protection is provided in the electrical power transformer rated more than 5mva. The principles of differential protection you must understand. One main difference between the pilot wire relay and the digital current differential relay is the.
The following are the classification of the differential protection relay. When internal cts should be connected to the same current coil of a faults occur in the transformer, immediate disconnection of differential relay in such an. Modern line current differential protection solutions schweitzer. The relay also features currentbased protection functions for remote backup for downstream protection relays and local backup for the line differential main protection. Until the advent of the highimpedance design, it was also applied to busbar protection, although the last few years have witnessed a. Lcb ii highspeed current differential relay system solid. However, the differential current can sometimes be substantial even without an internal fault. Differential protection is based on kirchhoffs laws, stating that all current into a network node shall add up to 0 in an ideal system.
Differential current protection of transformer using. Modern line current differential protection solutions. In a percentage restraint current differential relay, the oper ating current is the vector sum of the ct currents. A new approach to current differential protection for transmission. Furthermore, this relay contains a highimpedance differential. Generally differential protection is provided in the electrical power transformer rated more than 5mva. Differential relay power systems gate ee exam youtube. A failure in the line current differential hardware does not impact backup protection. Current differential line protection setting consideration. Differential protection what goes in must come out. Current differential protection another common form of protection for apparatus such as transformers, generators, busses and power lines is. Sel387 current differential and overcurrent relay protection protect power transformers with as many as four windings using. Phase comparison relays are line differential relays mainly intended for used with power line carrier.
Biaseddifferential protection theory and application eep. The relay whose operation depends on the phase difference of two or more electrical quantities is known as the differential protection relay. Abstractparalleling current transformers cts is a common practice in differential or line protection applications where the number of cts exceeds the number of relay current inputs. Differential protection is a unittype protection for a specified zone or piece of equipment. As a unit protection having its zone delimited by location of current transformers cts, the differential protection principle is considered superior. To overcome these difficulty, the percentage differential relay, or based differential relay is used. The differential protection of transformer has many advantages over other schemes of protection. The relay provides unit type main protection for overhead lines and cable feeders in distribution networks. Nov 01, 2016 a differential relay is defined as the relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined amount. The relay also features current based protection functions for remote backup for downstream protection relays and local backup for the line differential main protection. Abstractline current differential protection creates challenges for relay design and application. Explain challenges of transformer differential protection understand need for tap, phase, and zerosequence compensation and how they work understand how transformer differential relays are made secure for inrush and overexcitation transformer differential protection presentation objectives.
A clever solution to the problem of false 87 relay tripping due to transformer inrush current is called harmonic restraint or harmonic blocking. Differential relaying provides selectivity by providing a zone of protection with a circuit of interconnected cts. In the current differential scheme, there are two sets of current transformer each connected to either side of the equipment protected by differential relay. It may also be used for four circuit transformer protection figure 9 when only three. One main difference between the pilot wire relay and the digital current differential relay is the communication medium used. Thus, the maximum dissipation should not exceed 18008 or 225 wattseconds per half cycle. But the effect of even a rare fault may be very serious for a power transformer. Line current differential relay characteristic 1 type a line current differential relay the type a line current differential relay is designed to protect two or threeterminal transmission lines and has a.
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