- Low Voltage CTs
- Low Voltage VTs
- Metering CTs
- Three Phase CTs
- Relay Class Protection Current Transformers
- IEEE C57.13 and IEC Class CTs
- Split Core CTs
- Large Frame CTs
- Rectangle CTs
- Auxiliary/Summation CTs
- Medium Voltage Instrument Transformers
- Switchgear Style CTs
- Medium Voltage CTs
- Medium Voltage VTs -Three Phase
- Medium Voltage VTs -Single Phase
- Medium Voltage CPTs
- Bushing CTs
- Generator Style CTs
- Miniature and PC Mount 50 to 400Hz CTs
- Rogowski Coils & Sensors
- Oil Insulated CTs & VTs
ABOUT METERING TRANSFORMERS
Instrument transformers comprise a large category of current and potential transformers for various voltage, frequency, and physical size ranges. We have broken them up into several different groupings: low voltage, which are system voltages under 15kV; high frequency, operating frequency over 1kHz; and size ranges from board mount parts up to current transformers with window sizes of 254mm by 610mm. Read through the different types we supply below and use our Instrument Transformer RFQ Form to request a specific part to meet your requirements.
Metering Current Transformers
Metering CTs have accuracy rating at specified standard burdens called Accuracy Class. This defines the performance characteristics of a CT and the maximum burden allowable on the CT’s secondary. Metering CTs are designed to be extremely accurate from very low current to the maximum current rating of the CT. Revenue grade CTs are special type which are used by utility companies for billing purposes.Accuracy Class defines the performance characteristics of a CT which includes the maximum burden allowable. CTs can be further separated into two groups; Metering Accuracy CTs or Relaying Accuracy CTs, and can have ratings for both groups.
1. Rated Ratio Accuracy Rating - a number which is certified by the manufacturer to be accurate to within the rated ratio expressed as a percent.
2. Maximum Burden - This is the maximum burden or load that may be placed on the secondary without causing an error greater than the stated accuracy classification. For Metering Class CTs, burden is expressed as ohms/impedance.
We provide commercial grade, low cost current transformers with center window type (donut style) constructions. CTs are available in many different sizes with capabilities for measuring 50-400Hz and currents of 5A to 15000A. Typical burden ratings for IEC are 1.5 VA, 3 VA, 5 VA, 10 VA, 15 VA, 20 VA, 30 VA, 45 VA and 60 VA (special secondary currents are available). ANSI/IEEE burden ratings are B-0.1, B-0.2, B-0.5, B-1.0, B-2.0 and B-4.0.
A burden rating of B-0.2 means a CT can permit up to 0.2 ohms of impedance in the metering circuit, before its output current is no longer a fixed ratio with respect to the primary current.
Most models are available as U.L. recognized devices. They can be specified with or without mounting feet and the secondary can be leads, terminals, or per customer requirement.
- UPS systems
- Transfer switches
- Motor-generator sets
- Commercial sub-metering
- 3 CTs in one package for 3-phase metering
- Accurate measuring for metering/WATT/VAR
- Current sensing, recording, monitoring and control
- Control panels and drives
LOW VOLTAGE CTs - CURRENT TRANSFORMERS
These are 600V low voltage general purpose CTs for use in Switchgear, Panel boards, Control panels, Motor control centers, Engine generators, Transfer switches, UPS’, and other applications. IEEE/ANSI or IEC accuracy classes are available along with low cost models for high volume usage. A wide range of ratios from 50:5 to 5000:5 with 1 Amp or different secondary currents are available.CTs can be single or multi ratios, with or without secondary resistor, and with or without mounting feet. Various construction options are available based on application - Plastic case, Resin cast, Tape insulated, or Resin dipped. Secondary connections are available with terminals, pins, leads, with or without connectors.
LOW VOLTAGE VTs - POTENTIAL TRANSFORMERS
These are 600V low voltage VTs used for AC voltage measurement in Panel boards, Metering control panels, LV switchgear, Motor control centers, Engine generators, Transfer switches, UPS’, and other applications in a step-down environment, to monitor voltage. They are designed for connection line-to-line or line-to-neutral in the same manner as ordinary voltmeters. The secondary voltage bears a fixed relation with the primary voltage, so that any change in potential in the primary circuit will be accurately reflected in the meters, or other devices connected across the secondary terminals. Potential transformers can be used with voltmeters for voltage measurements, or they can be used in combination with current transformers for watt-meter or watt-hour meter measurements. They are used also to operate protective relays and devices, and for many other applications, and since they are used in a monitoring capacity, they generally require much greater accuracy in design.
Potential Transformers come in a wide range of ratios with secondary voltages 100/110/120V (different secondary voltages are possible). Single-phase or 3-phase designs are available in Plastic cased or Resin cast molded construction, with or without mounting brackets.Standard designs are 60Hz but 50 and 400Hz designs are available. IEEE/ANSI or IEC accuracy classes are available along with low cost models for high volume usage. A wide range of ratios from 50:5 to 5000:5 with 1 Amp or different secondary currents are available.
THREE PHASE CTs - CURRENT TRANSFORMERS
A 3-phase current transformer is made with three single-phase current transformers packaged together as one unit. They are usually encased in plastic or resin housing, and are typically used in motor control applications with 3-phase metering and overload protection applications. These CTs are compact and easier to install, compared to three single-phase CTs.
Various round and rectangle window options are available and are primarily used for 3-phase metering in MCC (motor control centers) for 3-phase relaying, metering, and overload protection.A wide range of ratios are available from 50:5 to 4000:5 in Plastic cased or Resin molded. Various secondary options are available - terminals or lead wires.
SPLIT-CORE CURRENT TRANSFORMERS
This type of current transformer is available to measure AC currents from 100 Amp to 3000 Amp, at 50 to 400Hz, with ratios from 50:5 Amp to 3000:5 Amp. Voltage output is possible with built-in resistor. These transformers are very popular in sub-metering applications, where existing systems are being upgraded and it is impractical to isolate the primary conductor. It is even possible to install this type of transformer while the conductor is energized; however, it is paramount that certain safety precautions be followed under such conditions. Rectangular in shape, standard split-core models are available with window dimensions up to 2.40" X 5.71". Larger, custom designed sizes are available by special order. Secondary burdens of 1.0 up to 50VA are common in split-core current transformers. Note that because of the split core construction, accuracy ratings are defined in part by the care in which the user installs the device.
LARGE FRAME CURRENT TRANSFORMERS
These are used for measuring 50-400Hz currents in bus bars and other large conductor systems. Typical configuration is 100A to 9000A primary current with secondary of 1 Amp or 5 Amp (special secondary currents are also available).Inside areas are as large as 8.06” x 22.06" x 27.00" and 12.80” x 13.58". All models come in an outer plastic case and are available with IEC Ratios/Accuracies, non-standard thermal rating, different encapsulation, or different secondary termination. CTs are UL, cUL Recognized and CSA Certified.
RECTANGLE CTs - CURRENT TRANSFORMERS
Hill Technical has an extensive range of rectangular current transformers, which are typically used for metering and relaying applications. Rectangle windows of the CTs can fit around primary bus bars or cables in applications where physical size and placement are very important. The secondary can be lead wires or terminals.
Rectangular CTs are used for measuring 50-400Hz currents from 100 Amp to 9000 Amp primary current with secondary of 1 Amp or 5 Amp (contact us for special secondary currents).Inside areas are as small as 1.69" x 0.43" and as large as 8.06” x 22.06" x 27.00" and 12.80” x 13.58". All models come in an outer plastic case and are available with IEC Ratios/Accuracies, non-standard thermal rating, different encapsulation, or different secondary termination. CTs are UL, cUL Recognized and CSA Certified.
AUXILIARY/SUMMATION CTs - CURRENT TRANSFORMERS
Summation CTs can have many different secondaries and are used to detect an unbalanced system condition typically due to fault. These have a wound primary with current ratings up to 50 Amps. The summation CTs converts 3-phase values into a single-phase value to operate a relay correctly. It accomplishes this by comparing the values derived from the current in the three phases of the primary circuit. It converts the 3-phase system into positive, negative, and zero sequence components. Current ratios range from 5:0.100 to 5+5+5+5+5:5.The line of the summation current transformer is connected to the primary of an auxiliary CT. Each line energizes a different number of turns on the primary side of the auxiliary CTs. The resulting single-phase output appears across the secondary. Various accuracy classes for metering or relaying and several sizes and ratios are available.