It is used for measurements of current and giving juice to the relays for pro. Typical burden ratings for IEC CTs are 1.5 VA, 3 VA, 5 VA, 10 VA, 15 VA, 20 VA, 30 VA, 45 VA & 60 VA. ANSI/IEEE burden ratings are B-0.1, B-0.2, B-0.5, B-1.0, B-2.0 and B-4.0. Calculating right burden VA for my application; Turns ratio of CT. CT should be as shown picture. Example 15.3 For part 2, 3, and 4 of Example 15.2, calculate the CT voltage if the phase relay burden is 1.2 , the residual relay burden is 1.8 , the lead resistance is 0.4 , and the CT resis-tance is 0.3 . Burden of Cable can be calculated as "Current Square x Resistance of cable per length x 2 times the length of cable" i.e Cable VA = (2L x R x I^2). Instantaneous overcurrent protection is where a protective relay initiates a breaker trip based on current exceeding a pre-programmed "pickup" value for any length of time. Calculation of the Current Transformer Accuracy Limit Factor Application Note. How to calculate burden of CT? CT internal resistance= 0.0332Ω, lead resistance=1.25Ω, relay burden=0.5Ω. This will give the value of pickup current. Let we calculate the burden resistor value, Look at the figure and apply Ohm's law, = Output Voltage across the burden resistor in volts R Burden = Burden resistance in ohms Is = Secondary Current flow Ip = Primary Current flow N is the Turns ratio, Hence, = Ip x R Burden / N Hence burden resistance will be The VA burden of the lead wires can be calculated by following mathematical formula. The burden includes the connected metering burden as well as the lead burden. 5/29/2015 Schweitzer Engineering Laboratories 29 Results of Repeated Faults and Mechanical Stresses E4C-130 -. What is Burden? Plug position is set at 2.5 times or 250% of rated CT current. NO. SEL-387 Current Differential and Overcurrent Relay AC Current Inputs (12 total) 5 A nominal 15 A continuous, 500 A for 1 second, linear to 100 A symmetrical Burden 0.27 VA @ 5 A 1 A nominal 3 A continuous, 100 A for 1 second, linear to 20 A symmetrical Burden 0.13 VA @ 1 A Frequency and Phase Rotation The Test engineer is doing CT burden test, for the CT 750/1 , he is injecting 1 Amp in the CT secondary wire, (at that time it is not connected to CT) , & we check in the relay 750 A ( the relay is 7UT6121), he is injecting 1 amp & voltage he gets is 2 v, so the burden= Volt * Amp. Calculate the actual primary current need to trip the relay. July 10, 2014 . Calculation of PSM Setting: From the figure shown below we can observe that, when the plug position is increasing, the time in seconds is decreasing. Electrical tools (MS Excel Spreadsheets) This section is dedicated to tools every electrical engineer can use in daily work.These spreadsheets below will make your job much easier, allowing you to shorten the time used for endless calculations of cables, voltage drop, various selections of circuit breakers, capacitors, cable size, and so on. A verification code will be sent to you. CT accuracy class. TRANSMISSION & DISTRIBUTION OF ELECTRICAL POWER. Clinical Imaging is a PubMed-indexed, peer-reviewed monthly journal publishing innovative diagnostic radiology research, reviews, editorials and more. NO. An example provided in IEEE C57.13 is 0.3 B-0.1 and B-0.2, 0.6 B-0.5. Refer to the table at the CT burden is the maximum secondary load permitted, expressed in voltamperes (VA) or ohms impedance, to ensure accuracy. Protective relay must be isolated from the high-voltage system but require current and voltage quantities proportional to those on the electric supply system. The calculation result is then inflated to be on safer side. - Burden on an instrument CT: That property of the circuit connected to . Introduction to the calculator. 2.10.3 No Accuracy versus Burden Calculation 26 2.10.4 Size 26 2.10.5 Weight 27 2.10.6 Safety 27 2.10.7 Simplified Ordering 28 2.10.8 Improved Switchgear Design and Performance 28 2.10.9 Environmental Aspects 29 2.10.10 Relay Design Simplification 29 RR is relay burden VS = I (RCT + RW + RR) Where I is the fault current and VS is the ct secondary voltage. CCN-Prbject-or ECP: SONGS 2 & 3 Calc No. XL, is adjustable to make the burden voltage VB be in phase with the phase-to-ground voltage of the system VS. The relay connected to the CT should operate for 60A of symmetrical primary current. Calculate the actual burden of the CT at 75°C: Solution: ƿ = 0.0216 µΩm (75°C) R = 0.0216 µΩm x (1.2 x 15 m) / 4 mm2 = 0.097 Ω However, while selecting the burden, one should be very careful as over estimation (more than required) may lead to selection of higher burden value. In general, there are three studies that can be considered for generator relay replacement ferroresonance evaluation. I didnt calculation involved in burden resistor and burden VA . Determine the burden of the device connected to the CT in VA or ohms impedance. The burden is shown as a resistor because, so far as it is possible, it is the practice to correct the power factor of the burden approximately to unity by the use of auxiliary capacitance burden. Where St=total burden in VA, Rct = internal resistance of CT secondary in ohm, Rw = wire (lead) resistance in ohm, Rr = relay resistance in ohm. Calculate the minimum primary current to just operate the relay? Position of Plug on a Relay. Method 1: Review of the existing system operation modes 2. The minimum required relay operate voltage setting (Vs) is given by: V S tI F (R CT R L ) u T (1) To ensure high speed relay operation the relay circuit operating voltage should be selected in accordance with the Dear all, I am building application for motor protection Relay. 5/29/2015 Schweitzer Engineering Laboratories 28 DO NOT DELETE Combined Transformer Bus and Feeder. C-3 of 47 --Pae I CALCULATION SHEET CCN CONVERSION: * | CCN NO. Relaying Current Transformer Application White Paper Relay Work Group . The burden voltage voltage is calculated at the CT secondary trip current rating and is calculated by multipling the total secondary burden resistance by the secondary relay trip current. This can be test switches and terminal blocks. Say current setting of the relay is 150 % therefore pick up current of the relay is 1 × 150% = 1.5 A. Step-3 Now we have to calculate PSM for the specified faulty current level. Substation-Design-Application. The total burden on secondary is due to the relays, meters, connecting leads and resistance of secondary winding of CT. CT burden can be reduced by using Continue Reading DP Aurosish Method 2 is a detailed procedure of selecting a control circuit transformer for a single relay or contactor and is important when other considerations are required, such as, high operating CT burden. For that, we have to first divide primary faulty current by CT ratio to get relay faulty current. Evaluating the performance of CTs and relays. The number after the letter B indicates the standard burden in Ohms at a power factor of 0.9. By Vijays Hiremath. definite time delay relay combined with a GE IAV55C inverse time characteristic relay . If the secondary burden is 0.33 ohms, the voltage required is 300x0.33, or 100 V. A CT with a relay rating of C200 or T200 should be chosen for this application. Subject: TLU Calc for Undervoltage Relay Circuits at Class 1 E 4 KV Swltchgear Sheet 5 of 47 The spreadsheet 'CT Saturation Calculator' is intended to provide quick indication not only of whether or not a CT will saturate in a particular application, but also an accurate indication of the actual waves-hape of the secondary current so that the degree of saturation as a function of time is apparent. setting is 100/5 A and the fault current is myths over CT calculation that still exist among the protection relay professionals: a) CT saturation is only caused by a high current associated with a high relay burden: False . Relay burden (Sr) The relay burden is the input current burden imposed by the relay on the current transformers. When the device is properly adjusted . For analog meter and electromechanical relay, the burden is stated on each equipment, but for numerical relay it is like only one value for all. Say current setting of the relay is 150 % therefore pick up current of the relay is 1 × 150% = 1.5 A. Step-3 Now we have to calculate PSM for the specified faulty current level. Lecture 16: PSM Setting and Phase Relay Coordination (Tutorial) Objectives In this lecture we will solve tutorial problems for PSM setting and relay coordination for phase fault. Calculate the total sealed volt-ampere burdens of all the devices that could be sealed . KNEE POINT CALCULATION The minimum knee point voltage for a given PS class CT is calculated by: Vkp = K*If(s)*(Rct+Rb). For example, while the Basler BE1-CDS220 is primarily a transformer differential relay (hence, includes the 87 device in elements named 87P Position of Plug on a Relay. The relay setting voltage must be made equal or Vkp stands for knee point voltage. PRATHYUSHA POWER PRIVATE LIMITED 10 MW BIO MASS BASED POWER PLANT CT / PT SIZING CALCULATION INPUT REF615 is a dedicated feeder protection and control relay for protection, control, measurement and supervision of overhead lines and cable feeders in utility. Salt Lake City, Utah 84103-1114 First, the calculation of the actual burden of the CT, including connection wires and protection relay impedance, is presented. If St is 25%-100% of rated burden of the CT, then the CT accuracy would be guaranteed, so in this way we can show (without calculating ALF) that the CT is Ok for the application. 21701-523-E-01 REV. The distance between the CTs and the protection relay is 15 meters, 4 mm2 Cu conductors in 4-wire connection are used. Relay operates for 60/10=6A of CT secondary current In order to make sure that the ct is in the linear range (to avoid ac saturation of the ct's), VS should be less than the knee-point voltage of the ct excitation characteristics. The control and protection system has an impedance is 0.1 . numeric relay generally contains many imple-mentations of these devices within its program-ming, and each instance of a device is referred to, herein, as an "element" in the relay. SHEET NO. ii) Operating voltage or relay burden expressed in voltage, V r. 2.2 Relay Setting Voltage The protection relay must remain stable under maximum through fault conditions, when a voltage is developed across the protection due to the fault current. The high burden may cause CT saturation. This is the simplest form of overcurrent protection, both in concept and in implementation (relay design). SWG_MANUAL. Before going into the impact of Burden on the performance of a Potential transformer, we will discuss about Burden. The standard ratings for protective relays are normally 5 A and 110 V, 50 Hz. The burden then includes the relay, CT wiring, and anything else between the CT and the relay. Fig.3 4. Relay Coordination (General Guides) ===== Sort in Other Section [TO DELETE] a; Relay Burden: The loading imposed by the circuits of the relay on the energizing power source or sources, expressed as the product of voltage and current (volt-amperes, or watts if D.C) for a given condition, which may be either at 'setting' or at rated current or voltage.The rated output . For that, we have to first divide primary faulty current by CT ratio to get relay faulty current. By Jhon Miranda. Download. First, let's go over some definitions that are related to currents transformers. 1 Beyond the Knee Point: A Practical Guide to CT Saturation Ariana Hargrave, Michael J. Thompson, and Brad Heilman, Schweitzer Engineering Laboratories, Inc. Abstract—Current transformer (CT) saturation, while a fairly common occurrence in protection systems, is not often clearly I am using Arduino board for interface. Relay = 0.5VA @ 5 A R R= VA/A2, R R= 0.5/25 = 0.02 Ω R W= 2 Ω(round trip) R CT= 0.20 Ω Total = 2.22 Ω Burden Calculation Example Differential Protection Setting Calculations Assume maximum secondary current of 90A and wye CTs V S = I (R CT+ R W+ R R) * (FΔ-Υ) -(FΔ-Υ) = delta or wye CT factor - Use 1 for wye; use 1.73 for delta V Solution: 1. This post will go over the application and theory of current transformers (cts) for protective relaying. Where 30% of the minimum fault current is more than the full load . The primary operating current of busbar protection is normally between 2% and 10% of the stability level i.e. If multiple meters/relays are connected then individual VA may be added in series to determine the total VA loading. E - CT ADEQUACY CALCULATION - VA REQUIRED = RELAY Burden + Lead Burden = RELAY Burden + (2 * Rl') Available Required E-1 = Rr + ( 2 X Rl') VA VA 20 5. ANSI standards list burdens of 2.5 to 45VA at 90% power factor (PF) for metering CTs, and 25 to 200VA at 50% PF for relaying CTs. By Salman Ijaz. However, almost all the relay technical literature indicates formulas for CT sizing with Class P as well as Class PX CTs. This is a calculated value which takes into account the burden (resistance) of the relay, resistance of the CT windings and resistance of the leads: R ct - secondary winding d.c. resistance at specified temperature ; R b - rated resistive burden of the relay ; R ' b - Rleads + Rrelay; this is thel connected burden In the calculation CT accuracy, the burden included in terminal ct such as wire, ct, relay, watt meter, power factor meter and etc. The relay connected to the CT should operate for 60A of symmetrical primary current. If the 10% secondary voltage cause 50% increase in the current then the CT is said to be saturated and the point is called knee point voltage of CT. Relay operates for 60/10=6A of CT secondary current ie, 2 * 1 = 2 VA , he calculates, on CT 15 VA is marked. From current setting we calculate the trick current of the relay. ♦ Relay errors: ±5%. If the knee point voltage calculated on the basis of the power network is higher than the specified knee point voltage of CT, then there is a chance of CT saturation during a fault in the power network, and probably the protection relay will not operate. The CT winding resistance from Figure 1 is 0.116 ohms. Find out the maximum secondary burden that can be used and still maintain rated accuracy at 20 times rated symmetrical secondary current if a 1200:5 C 400 CT is connected on 800/5 tap. Plug position is set at 2.5 times or 250% of rated CT current. 1. Neglect CT saturation and lead wire resistance. Effect of fault type on CT burden. Based on the above calculation, check the rated knee point voltage of CT. Calculate the actual primary current need to trip the relay. Answer: Number of turns =50/5=10. **broken link removed** I have attached image of CT which planning to. CT internal resistance= 0.0332Ω, lead resistance=1.25Ω, relay burden=0.5Ω. The burden is shown as a resistor because, so far as it is possible, it is the practice to correct the power factor of the burden approximately to unity by the use of auxiliary capacitance burden.
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