Overview
The PR series dry-type current transformers are precision electromagnetic instruments designed for accurate current measurement, energy metering, and relay protection in 0.66kV low-voltage AC power systems. Operating on Faraday’s law of electromagnetic induction, they provide galvanically isolated secondary current signals proportional to the primary current, ensuring reliable performance in industrial and distribution applications.
These bushing-type CTs feature a toroidal magnetic core with the primary conductor passing through the aperture and secondary windings wound around the core, delivering standardized 1A or 5A output for connected instrumentation and protection devices.
Key Ratings Snapshot
| Item | Specification |
|---|---|
| System voltage class | 0.66 kV |
| Rated frequency | 50 Hz or 60 Hz |
| Rated secondary current | 1 A or 5 A |
| Accuracy classes | 5P10, 10P10, 5P20, 10P20 |
| Rated burden | 2.5 VA to 30 VA (typical) |
| Burden power factor | cos phi = 0.8 (lagging) |
| AC/BIL insulation level | 4 kV / 10 kV |
| Primary terminals | P1 / P2 (bushing type) |
| Secondary terminals | S1 / S2 (lead wires or screw terminals) |
| Multi-ratio capability | Available with tapped windings |
Construction
The PR series features a dry-type bushing (ring-type) structure with customer-selectable insulation: epoxy resin cast for superior moisture resistance and mechanical strength in air or SF6 environments, or insulation tape wrapping suitable for oil-immersed installations where transformer oil provides additional dielectric support. The toroidal magnetic core ensures optimal electromagnetic performance and minimal phase error.
Designed for installation in gas-insulated switchgear (GIS) with SF6 or air, or within power transformer bushings immersed in oil, the CT accommodates secondary terminations via lead wires or screw terminals based on project requirements. Terminal markings follow IEC 61869-2 polarity conventions (P1/P2, S1/S2) to ensure correct metering and protection functionality.
Technical Parameters
Service Conditions
- Installation environment: Indoor switchgear, outdoor enclosures, or submerged in transformer oil
- Altitude: Not exceeding 1000 m above sea level
- Ambient temperature: -25 degC to +55 degC (air); per oil spec (oil-immersed)
- Relative humidity: Daily average <= 95%, monthly average <= 90% (at +20 degC)
- Environmental conditions: Free from corrosive gases, explosive media, severe vibration, or mechanical shock
Technical Data
| Parameter (Selection-Oriented) |
Specification |
|---|---|
| Protection accuracy classes | 5P10, 10P10 (standard); 5P20, 10P20 (on request) |
| Rated secondary current | 1 A or 5 A |
| Rated burden range | 2.5 VA to 30 VA |
| Multi-ratio capability | Available with tapped secondary windings |
| Insulation level (AC/BIL) | 4 kV / 10 kV |
| Frequency | 50 Hz or 60 Hz |
Installation & Wiring
Installation Diagram
The PR series CT is installed by passing the primary conductor or bushing through the central aperture. Secure mounting using brackets or supports is required. For oil-immersed applications, full submersion in transformer oil with adequate circulation is essential. In SF6 GIS, gas pressure and purity must comply with switchgear manufacturer specifications. Maintain clearance for secondary wiring access and serviceability.
Outline Dimensions
| Dimension | Value |
|---|---|
| Aperture diameter (phi) | As specified per order (matches bushing/conductor) |
| Overall outer diameter | Per custom drawing |
| Height | Per custom drawing |
| Secondary terminal location | As shown on certified dimensional drawing |
Selection & FAQs
Selection Guide
- Define the installation medium: air-insulated switchgear, SF6 GIS, outdoor enclosure, or transformer oil.
- Select the ratio and 1A or 5A secondary from the protection study and relay input.
- Choose 5P10/10P10 or request 5P20/10P20 according to protection sensitivity and fault-current requirements.
- Calculate relay and cable burden and specify a suitable 2.5VA–30VA rated output.
- Confirm aperture, insulation system, multi-ratio taps, mounting, terminals, grounding, and certified drawing.
Frequently Asked Questions
Q1: What accuracy classes are available for this protection CT?
Standard classes include 5P10 and 10P10, with 5P20 and 10P20 available on request. Specify your required accuracy limit factor and burden during inquiry.
Q2: Can this dry-type CT be installed outdoors or submerged in oil?
Yes, it supports indoor, outdoor enclosure, or oil-immersed installations. Ensure the ambient temperature remains between -25°C and +55°C for air, or follows oil specifications.
Q3: How can I achieve multiple current ratios with a single unit?
Multi-ratio capability is available using tapped secondary windings. Provide your primary and secondary ratio requirements to the engineering team for custom winding design.
Q4: Which factory tests are performed before shipment?
Standard routine tests are conducted prior to dispatch. Contact us for detailed test reports or specific certification requirements.
Q5: Is the rated burden customizable beyond 30 VA?
The standard rated burden range is 2.5 VA to 30 VA. For higher burden requirements, please contact our technical team for custom design feasibility.
Q6: Where are these 0.66kV current transformers typically applied?
This 0.66kV dry-type current transformer is designed for low voltage protection in indoor switchgear and outdoor enclosures. It supports standard 50 Hz or 60 Hz power systems.
Q7: Does this CT meet standard low voltage insulation requirements?
Yes, the unit features an AC insulation level of 4 kV and a BIL of 10 kV. Verify these ratings against your specific switchgear clearances during the design phase.