Instrument Transformers

Overview

Instrument transformers scale high voltages and currents down to levels that meters, relays and digital substation equipment can safely use. Raptronics supplies a complete portfolio by PFIFFNER, including current transformers (CTs), inductive voltage transformers (VTs), capacitor voltage transformers (CVTs) and RC dividers, from MV through EHV applications.

Every protection decision and every revenue invoice in a substation depends on the signal these transformers deliver. A CT that saturates during a fault, or a VT with the wrong accuracy class, can cause a relay to trip when it should not or a meter to bill the wrong amount.

Our engineers help utilities, OEMs and EPCs choose the right type, ratio, accuracy class and burden for each application, and check that the selection matches the protection scheme and the metering rules that apply.

Specifications

Product range

CTs, inductive VTs, CVTs, RC dividers

Types

• Current transformers (CTs)

  CTs produce a secondary current proportional to the primary current, for metering and protection. Protection cores have to stay accurate during fault currents many times higher than normal load, while metering cores need to be precise around normal load.

• Inductive voltage transformers (VTs)

  Inductive VTs, also called potential transformers, step the line voltage down using a wound magnetic core. They are widely used for metering and protection, particularly where high accuracy is required.

• Capacitor voltage transformers (CVTs)

  CVTs use a capacitive divider followed by an inductive stage. At high and extra high voltages they are often more economical than inductive VTs, and the capacitor stack can also be used to couple power line carrier signals onto the line.

• RC dividers

  RC dividers combine resistive and capacitive elements to give a wide frequency response. That makes them suited to digital substations and HVDC, where the measurement has to capture fast transients and harmonics, not only the fundamental frequency.

Applications

• Revenue metering

  Billing points between utilities, generators and large industrial customers, where accuracy class and approval for revenue use matter.

• Protection & control

  Line, transformer and busbar protection schemes, where the CT and VT must perform correctly during faults and transients.

• Digital substations & HVDC

  Installations using merging units and process bus, and HVDC converter stations, where wide bandwidth measurement is needed.

Applicable standards

We carry the applicable standards for your voltage class. Please reach out with your inquiries for more details.

Frequently asked questions