Modern line current differential protection solutions schweitzer. Bus protection, automatic reclosing, 292 by backup relays, 275, 291 circuitbreaker bypsasing, 292 combined power transformer and bus, 287 current differential with overcurrent relays, 278 current differential with overvoltage relays, 288 current differential with percentage relays, 284 directional comparison, 277 fault bus, 275 grounding. Busbar protection busbar differential protection scheme. Standard configurations d and e include directional overcurrent and voltage based protection functions. The differential protection used for power transformers is based on merzprize circulating current principle.
Use overcurrent elements from combined ct inputs for backup protection. Sel387e current differential and voltage relay schweitzer. The scheme of busbar protection, involves, kirchoffs current law, which states that, total current entering an electrical node is exactly equal to total current leaving the node. Differential protection principle differential overcurrent protection. Two or threewinding power transformers can be included in the protected zone. Current, voltage, directional, current or voltage balance, and differential relays chapter 2 described the operating principles and characteristics of the basic relay elements. In systems where over current or distance protection systems are present, busbars will be inherently protected. Red650 line differential protection substation automation.
Voltage inputs for power metering, overexcitation protection, and overunderfrequency load shedding provide versatile solutions for power apparatus protection. So what to do to prevent tripping because of the differential current caused by the above mentioned reasons. Differential protection of transformer differential relays. Bus protection l over current l differential l backup l under voltage. Choose from common or independent harmonic blocking or restraint.
Pdf a currentbased solution for transformer differential. The highimpedance input is created by an internal impedance, typically resistive, of 2000 ohms or higher. For the biased differential protection the following measurement quantities are used. May 15, 2018 at maximum through fault current, the spill output produced by the small percentage unbalance may be substantial. As a unit protection with its zone constrained by location of current transformers cts, the differential protection principle is considered superior. Easy to integrate and with an extensive function library, the relion family of protection and control delivers advanced functionality and.
Multiwinding current differential protection apply the sel387 relay for protection of two, three, or fourwinding power transformers. Diff current differential protection is a fast, selective method of protection against short circuits. The relay is adapted for the protection of overhead. Percentage restrained differential, percentage of what. Sep 08, 2016 observation of ref stability are as under. 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. Differential protection is a unittype protection for a specified zone or piece of equipment. This video outlines the basic principles behind differential protection and is a sample of the full 2. Apply subcycle current differential protection with included fourzone distance and directional overcurrent backup.
Modern line current differential protection solutions hank miller and john burger, american electric power normann fischer and bogdan kasztenny, schweitzer engineering laboratories, inc. This section includes the following overviews of the sel311l relay. Protective relays, associated communication systems, voltage and current sensing devices. Figure 1 shows a simple differential protection scheme, also known as a merzprice scheme in this simple scheme, we can assume that under normal operating conditions, the current entering into the piece of equipment under protection is equal or in the case of a transformer, proportional to its exiting current. It can precisely determine if the fault is within the.
For this reason, differential protection is often applied to highvalue apparatus such as transformers, large motors, and generators. To prevent the differential protection scheme from picking up under such conditions, a percentage differential protection scheme is used. Aug 31, 2018 in current differential protection of busbar, if ct secondary circuits, or bus wires is open the relay may be operated to isolate the bus from live system. The principles of differential protection you must understand. Patel ge power management malvern, pa presented at the electric council of new england. Sel311l line current differential protection and automation. Use single or dual differential channels for reliability. A differential protection relay is defined as the relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined amount.
Jun 23, 20 in differential protection scheme, the current entering at one end of the line and leaving from other end of the line is compared. A new approach to current differential protection for. A failure in the line current differential hardware does not impact backup protection. Traditionally, current differential protection communication channels are either direct fiber optic cable or multiplexed. Figure 1 shows a simple differential protection scheme, also known as a merzprice scheme. Line differential protection substation automation. Pdf differential protection schemes and techniques for power. The slope characteristic provides high sensitivity when low levels of current. Pdf line current differential protection creates challenges for relay design and application. Therefore, differential protection of transformer should be provided with a proportional bias of an amount which exceeds in effect the maximum ratio deviation. Under normal working condition, the two currents at both ends are equal and pilot wires do not carry any current, keeping relays inoperative. Busbar protection, differential protection, dynamic zone selection. T60 percent differential calculations ge power management 3 slope 2 identifies the slope where the ct saturation are likely and maximum restraint is required.
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. The example differential protection relay shown in the below figure is a transformer differential relay. Abstractpercentage restrained differential protection is one of the oldest forms of adaptive protection algorithms. All protectiverelay types are derived either directly from these basic elements, by combining two or more of these elements in the same enclosing case or in the same. As a unit protection having its zone delimited by location of current transformers cts, the differential protection principle is considered superior.
The differential relay works on the principle of comparison between the phase angle and magnitude of two or more similar electrical quantities. Differential protection for arbitrary 3ph power transformer. As a unit protection with its zone constrained by location of current transformers cts, the differential protection principle is considered superior with respect to selectivity, sensitivity, and. Line differential protection siprotec 5 siemens global. It does not need coordination with other relays, however, it lakes to have backup protection. The relay also features current based protection functions for remote backup for downstream protection relays and local backup for the line differential main protection. A typical dc circuit for busbar differential protection scheme is. Principles of differential relaying current balance high impedance also known as unbiased differential protection only one actuating relay quantity current required for operation. A currentbased solution for transformer differential. Use the sel311l line current differential relay with integral fourzone distance backup for easytoapply, highspeed line protection.
For this reason transformer differential relays are said to percentagedifferential relays. Digital current differential relays power line carrier figure 1. The red650 features phasesegregated current differential protection with excellent sensitivity for high resistive faults and secure phase selection for up to three line terminals. The relay whose operation depends on the phase difference of two or more electrical quantities is known as the differential protection relay. A pair of identical current transformers are fitted on either end of the section to be protected alternator winding in this case. The 87l function of the sel411l provides protection for any transmission line or cable with as many as three terminals over serial communications and. Hence, total current entering into a bus section is equal to total current leaving the bus section.
Differential protection is the best technique in protection. Line current differential relay response to a direct. A new approach to current differential protection for transmission lines m. What this practically means for a line protection application is that the current that is measured. Voltage applied hv rph 230v measured current hv ct differential core 12ma hv nct current 12ma current measured at hv ref relay terminal 0. The value of the operate current has to be a certain set percentage higher than the current flowing in the restraint coils. Transformers and compensating coils in the protection range are also possible. Percentage differential protection slope in differential. Differential protection what goes in must come out. This course explains protection relay selection process by detailing how to protect against each fault type or abnormal condition. Differential protection electrical impedance relay. It implies that a large differential current is required for an. Differential protection schemes are mainly used for protection against phasetophase fault and phase to earth faults.
It is fair to say that the first introduction of bus zone protection in euro pe started in britain as early as 1904. Differential protection protection of transformer, motor. A sensitive current element in series with the highimpedance element is calibrated in volts based on the voltage drop across the internal impedance. Current differential line protection current differential relaying is a method of extending the benefits of differential protection as applied to transformers, buses or generators to the protection of transmission lines. Abstract digital current differential protection has the advantages of application simplicity, operation speed, and high sensitivity.
Pdf modern line current differential protection solutions. Designed to seamlessly consolidate functions, relion relays are smarter, more flexible and more adaptable. A typical dc circuit for busbar differential protection scheme is given below. Bus protection considerations for various bus types. Current comparison relays with associated communication media current differential line protection current differential relaying is a method of extending the benefits of differential protection as applied to transformers, buses or generators to the protection of transmission lines.
For generator differential protection, one set of current transformers ct are located on generator neutral side, whereas second set of ct is located on generator phase side. In electric current differential protection of busbar, if ct secondary circuits, or bus wires is open the relay may be operated to isolate the bus from live system. Channels traditionally used for line current differential. Current differential line protection setting consideration. Line current differential protection current differential protection is based on kirchhoffs current law, which states that the sum of all measured currents that make up a protected zone must equal with zero,the protected zone being defined by the location of current transformers cts. Generally differential protection is provided in the electrical power transformer rated more than 5mva. An alternative principle for line protection that is quickly becoming the norm is differential protection. L to limit current through relay to differential protection j. The differential protection of transformer has many advantages over other schemes of protection. Pdf differential protection of power transformer in substation. Learn the basics of differential protection of transformers. Sel387 current differential and overcurrent relay protection protect power transformers with as many as four windings using.
Twowinding current differential protection sensitive current differential protection with programmable single or dualslope percentage restraint, supervised by the second and fifthharmonic elements for secure differential protection on twowinding apparatus. Seriescompensated and long linesprevent zone 1 overreach on seriescompensated lines with optional logic in the sel411l1 advanced line differential protection, automation, and control system. Conventional current differential protection needs to be set above ich to avoid tripping for 5060hz line charging current modern relays can extract ich to allow more sensitive current settings to be applied protection of transformer feeders. 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. Principles of differential relaying my protection guide. Electrical faults l phase to phase l phase to ground l phase to phase to phase l phase to phase to phase to ground. The differential protection used for power transformers is based on merzprice circulating current principle. Sel411l advanced line differential protection, automation. It works on the principle of comparison between the phase angle and the magnitude of the same electrical quantities. Mohammed tawfeeq alzuhairi 321 differential protection differential protection is the best technique in protection. Participants at the time this draft was completed, the d32 working group had the following membership. The sel387e current differential and voltage relay provides protection to two or threewinding power transformers.
Twowinding differential protectionprovide current differential protection with programmable single or dualslope percentage restraint for twowinding transformers, reactors, generators, large motors, and other twoterminal apparatus. Real time simulation of cts in a current differential protection scheme. Pdf advanced line current differential protection with reduced. Such protection provides protection against internal phasetophase and phasetoearth faults and is generally used for transformers of rating exceeding 2 mva. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. The locations of current transformers cts define the boundary of a differential protection zone. Therefore, it is necessary to stabilize the differential current pr otection by means of a so called bias current. Differential protection is applicable to all parts of the power system. Partial differential relaying sums the currents entering or leaving a switchgear bus through main and tie breakers. It is based on the fact that it is only in the case of faults internal to the zone that the differential current difference between input and output currents will be high. If the net difference equal zero, it means no fault exist. Therefore, differential protection of transformer should be provided with a proportional bias of an amount.
Thompson, schweitzer engineering laboratories, inc. Introduction the bus zone protection has experienced several decades of changes. 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. In differential protection, cts are oriented so that a line drawn from the polarity mark to the protected equipment passes through the ct. In this type of protection the electrical quantities entering and leaving the protected zone or area are compared by current transformers c. Sel587 current differential relay schweitzer engineering. The principle of differential busbar protection is very simple. A current based solution for transformer differential protection part i. Transformer differential relays haverestraint coils as indicated in figure 1. This was known as the circulating current merzprice system 7. At maximum through fault current, the spill output produced by the small percentage unbalance may be substantial.
It is assumed with these schemes that a certain degree of ct saturation is possible under throughfault conditions. Modern line current differential protection solutions. A new approach to current differential protection for transmission. Pdf line current differential protection automation and. It should be noted that over current protection will only be applied to relatively simple distribution systems, or as a backup protection, which gives a considerable. 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 relay current differential relay biased beam. Based on principle of merz price circulating current, differential protection is a complete earth and phase fault protection. It will respond to all internal faults and ignore all external through faults and load flow.
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. Differential protection of transformer differential. Differential protection for detecting internal faults is an attractive option for transformer because. If a fault exists on the protected bus, the currents will add in the relays, but if fault current is. 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. So differential protection will operate which is not expected to operate for the above said reasons. Abstractline current differential protection creates challenges for relay design and application. In a percentage restraint current differential relay, the oper ating current is the vector sum of the ct currents. The principles of differential protection you must. Modern design principles for numerical busbar differential. The siprotec 7sd828687 line differential protection have been designed particularly for the selective protection of overhead lines and cables with singleended and multiended infeed in mediumvoltage and highvoltage systems. Protection relays differential relays b high impedance differential protection. Alexander ge corporate ge power management research and development malvern, pa schenectady, ny updated and presented by subhash c. Line differential protection psl 6603u product guide.
Applying digital line current differential relays over pilot. Builtin charging compensation improves the sensitivity and speed of differential protection for long lines. The current waveforms for the currents of each phase. Differential relay current differential relay biased. The protection for internal fault in such type of transformer is to be provided by using differential protection system. Problem statement article pdf available in ieee transactions on power delivery 164. Applying digital line current differential relays over pilot wires 73 1. Vectorial correction virtual interposing ct virtual interposing ct. Differential protection i 1p i 1s ct1 20005 a i 2p i 2s bus ct2 20005 a h1 x y. Problems for the differential protection caused by transformer inrush currents are discussed. The mathematical relationship between differential protection and directional protection is derived. The introduction of digital technology has led to further improvements in bus differential. Line current differential protection automation and control system.
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