Current & Instrument Transformers

Transcription

1 Reliable & Accurate Inputs for Measuring & Protection Equipment Current & Instrument Transformers Type MKE11 Inside the Catalogue Range Specifications Ordering Code Delivering Value to You

2 M-Kris Electric is a new firm in electrical sector committed to provide quality and reliable products and solutions to its customers for improving the performance of electrical systems. The current range of M- Kris includes current and instrument transformers and electronic devices (timers, power analysers, phase monitoring relays, earth leakage relays, digital meters etc.). Introduction Seemingly obscure and unsung, these are behind the scene electrical products which form the crucial link between the electrical system and protection & control devices. The accurate and reliable performance of these instrument transformers over a period of time is the key to the well being of the electrical system as a whole. Typical applications of instrument transformers are in switchboards for use with measuring instruments like ammeters, energy-meters, multi function power analyzers, and protection devices such as overload relays, earth fault and earth leakage relays, protection relays etc. M-Kris Instrument Transformers are designed and manufactured in accordance with relevant IEC standards and available in standard configurations as well as custom specifications. Functions of Instrument Transformers Principle of Operation All the current based instrument transformers work on the principle of constancy of ATs (ampere-turns) i.e. higher current in the primary can be transformed to lower current simply by increasing the number of turns in the secondary winding. Thus a suitable number of turns are provided in the secondary circuit to bring the current to manageable level for metering and protection purposes. Though technically speaking, ATs remain equal on both the primary and secondary, in reality, some losses happen in magnetizing the core and heating of winding. These losses lead to ratio error and phase error. Quality of core and winding material determines the quantum of error.

3 Range - at a glance Low Voltage Current Transformers Extensively used in low voltage switchboards, the LVCTs transform the line currents to appropriate levels making them suitable for use with measuring instruments and protection devices. It is clear that accuracy of these current transformers is critical for reliable operation of these measuring instruments and protection devices. Classification LVCTs can be classified on the basis of construction, material, function, shape: Function: Metering / Protection Material: Tape wound / Resin cast / Nylon casing / ABS moulded Construction: Wound primary / bar Shape: Round / Rectangular Metering CTs are specified with the accuracy class of 3, 1, 0.5 or 0.2. Lower number indicates higher level of accuracy. Metering CTs are required to transform the primary current in the current range from 5% to 120% of its rated primary current, within the tolerance limits specified by its accuracy class. Metering CTs must saturate above 120% of the rated primary current to prevent damage to the measuring instruments connected to the secondary of the CT. VA capacity of the CT specifies the maximum level of VA burden of devices / instruments on the secondary circuit of the CT e.g. it will be inappropriate to use a 2VA CT for a measuring device having VA burden of 4VA.

4 User benefits for M-Kris CTs Wide range helps in selecting the right CT for the application Size of aperture/opening accept all the sizes of busbars/cables Minimum space requirement VA Capacity wide range from 1VA to 15VA helps in matching closely the CT and the device Low losses lesser heating and hence lesser deterioration of CT leading to its longer life Selecting the accuracy class for Metering CTs Application Recommended Accuracy Class Calibration 0.2 Tariff based metering 0.5 Non-tariff sub metering 1.0 General purpose measurements Indicative measurements

5 Selection Charts MKE1106M Metering CT upto 600/5A MKE1106S Metering CT upto 600/5A MKE1107M Metering CT upto 750A Class 1 CT Ratio Class 1 Class 3 60/5A to 80/5A VA 1 100/5A VA 1 125/5A VA 1 150/5A VA /5A VA /5A VA /5A VA /5A to 600/5A VA 5 RATIO Class 1 Class 3 60/5A to 80/5A VA 1 100/5A VA 1 125/5A VA 1 150/5A VA /5A VA /5A VA /5A VA /5A to 600/5A VA 5 RATIO Class 1 Class 3 50/5A VA /5A VA /5A VA /5A VA /5A to 750/5A VA 5 MKE1108S - Metering CT upto 800A RATIO Class 0.5 Class 1 Class 3 150/5A VA /5A VA /5A VA /5A VA /5A VA /5A to 800/5A VA 5 7.5

6 MKE1108M - Metering CT upto 800A RATIO Class 1 Class 3 150/5A VA /5A VA 5 250/5A VA 5 300/5A VA 5 400/5A VA /5A to 800/5A VA 7.5 MKE1116S - Metering CT upto 1600A RATIO Class 0.5 Class 1 400/5A VA /5A VA /5A VA /5A VA /5A VA /5A VA /5A to 1600/5A VA 15 MKE1120M - Metering CT upto 2000A RATIO VA Class 0.5 Class 1 400/5A VA /5A VA /5A VA /5A to 2000/5A VA MKE1140S - Metering CT upto 4000A RATIO Class 0.5 Class 1 400/5A VA 5 500/5A, 600/5A VA /5A, 800/5A VA /5A to 1600/5A VA /5A, 2500/5A VA /5A VA /5A VA 30

7 Medium Voltage Current Transformers Available upto 33kV. Double ratio triple core CTs are also available Specifications: Parameter Voltage Primary current Secondary Current Insulation Level Class of Insulaton Value 3.3/6.6/11/33 kv 10A to 2000A 1A / 5A 30kV F Core Balance Current CT (CBCT) Also called Zero Sequence Current CTs, the CBCTs work on the summation principle of current that the vector sum total of currents in three phases at any point should be zero. However, this condition gets violated in case of earth fault and earth leakage when part of the current leaks into earth. CBCTs detect this abnormal condition and give an output current in the secondary circuit. Specifications: Leakage current: 300mA, 1A, 3A, 5A Construction: Tape wound / Resin Cast Aperture: As per customer requirement (round/rectangular) Summation Current Transformers When the currents in multiple feeders need not be individually metered but their combined value needs to be monitored, a summation current transformer is used. The summation CT consists of two or more primary windings which are connected to the feeders to be summated, and a single secondary winding, which feeds a current proportional to the summated primary current. A typical ratio would be 5+5+5/ 5A, which means that three primary feeders of 5A are to be summated to a single 5A meter. Secondary currents of 1A are also used. Specifications: Parameter Value Primary current 1 5A Secondary current 1 or 5A Accuracy class 0.2, 0.5 or 1 VA Burden 1 to 30VA Mounting Inserts for base mounting

8 Voltage Transformers Also called PTs (potential transformers), these instrument transformers are used for stepping down the voltage to 110V (usually) for compatibility with the measuring and protection devices. Specifications for VTs/PTs: Parameter Construction Primary Voltage Secondary Voltage Accuracy Class Burden Overvoltage factor Neutral Connection Specified Values Resin Cast / Oil type 3.3/6.6/11 kv 110/ 3 V, 110V 0.2, 0.5, 1.0 for metering and 3P for protection Upto 200VA 1.2 continuous, 1.5 for 30 sec for effectively earthed system and 1.9 for 8 hours for non-effectively earthed systems Connected to earth Y/Y, Y/ COMBINED CT-PT UNITS Also called metering units, these can be offered in dry type/oil immersed dry type being primarily used for indoor applications and oil type for outdoor applications. The metering unit may consist of: 2 nos. single phase CTs and 1 no. three phase PT 3 nos. single phase CTs and 1 no. three phase PT 2/3 nos. single phase CTs and 3 nos. single phase PTs Note: Please contact us for technical details of Tape Wound and Resin Cast Current Transformers. Custom built CTs, Control Transformers and Interposing CTs also available. Other products offered by M-Kris Electric: ELR Digital Panel Meters Timers Power Analysers Protection Relays Process Indicators Motor Starters Wires & Cables M-Kris Electric 383, Shriniketan Plot-1, Sec-7, Dwarka, New Delhi INDIA Phone/Fax: mkris.ele@gmail.com Web: Specifications subject to revision without prior notice.