LZZBJ9-35/250, LZZB8-35Q Indoor Epoxy Cast-Resin Current Transformer

Product Overview

The LZZBJ9-35/250-I / LZZB8-35Q indoor support-type current transformer is a fully enclosed epoxy resin cast current transformer designed for 35kV / 36kV / 40.5kV indoor medium-voltage power systems. It is suitable for AC power systems with rated frequency of 50Hz or 60Hz and is used for current measurement, energy metering and relay protection in medium-voltage switchgear, distribution cabinets and power measurement panels.

This product is part of the 35kV-class LZZBJ / LZZB indoor pillar CT platform. The key structural feature is the 250mm epoxy casting body width. In the model code, 250 refers to the cast-resin body width / product body width, which directly affects cabinet matching, insulation clearance, conductor layout and terminal access. The LZZBJ9-35/250-I and LZZB8-35Q are positioned for indoor air-insulated switchgear where a compact but high-insulation support-type CT is required for 35kV / 36kV / 40.5kV systems.

Product Type

Model Explanation

• L: Current transformer.
• Z: Support-type / pillar-type structure.
• Z: Epoxy resin casting insulation.
• B: Current transformer series with metering and protection winding options.
• J: Reinforced / protection-capable structure reference.
• 9: Design sequence / product platform code.
• 35: 35kV product class, suitable for 35kV, 36kV and 40.5kV systems.
• 250: Epoxy casting body width, meaning the cast-resin product body width is 250mm.
• I: First structural version / type variant of 35kV CT platform.

Applications

• 35kV, 36kV and 40.5kV indoor medium-voltage AC power systems
• Air-insulated switchgear and indoor distribution cabinets
• Current measurement for incoming and outgoing feeder circuits
• Energy metering and power measurement panels
• Relay protection for feeders, transformers and bus sections
• Industrial substations, utility substations and power distribution rooms
• Projects requiring a 250mm cast-resin body width for cabinet layout and insulation coordination
• Indoor systems requiring combined metering and protection secondary windings

Features

• 250mm body width: The 250mm cast-resin width gives a clear mechanical reference for switchgear layout and product selection.
• 35kV-class insulation platform: 40.5/95/185kV insulation level supports 35kV / 36kV / 40.5kV international voltage classes.
• Fully enclosed epoxy casting: The primary winding, secondary winding and magnetic core are sealed inside the resin body for improved insulation stability.
• Support-type structure: Suitable for indoor switchgear mounting and stable mechanical support.
• Good moisture resistance: The epoxy cast-resin body helps improve moisture resistance and long-term indoor reliability.
• High safety operating margin: Designed for reliable operation in medium-voltage switchgear under normal indoor service conditions.
• Metering and protection functions: Supports current measurement, energy metering and relay protection in one CT platform.
• Customizable parameters: Current ratio, accuracy class, rated output and winding configuration can be produced according to project requirements.

Structure Overview

The LZZBJ9-35/250-I / LZZB8-35Q current transformer adopts an epoxy resin cast insulated and totally enclosed pillar-type structure. The product body is formed by casting the windings and core assembly into the epoxy resin insulation body. This structure provides strong insulation performance, good moisture resistance and a higher safety operating coefficient for indoor medium-voltage switchgear.

The primary outlet terminals are marked P1 and P2. Secondary terminal groups are arranged according to the number of windings, such as 1S1, 1S2, 2S1, 2S2 and other project-specific terminal markings. The actual terminal arrangement shall follow the approved wiring diagram and product nameplate.

Operating Principle

The current transformer converts primary current in a 35kV / 36kV / 40.5kV circuit into a standardized secondary current, normally 5A or 1A. The secondary signal is connected to meters, measuring instruments, protection relays or monitoring equipment, allowing the system current to be measured safely and used for protection control without direct connection to the high-voltage primary circuit.

For metering applications, the CT should maintain ratio error and phase displacement within the selected accuracy class and rated burden. For protection applications, the protection winding must provide reliable secondary output under fault-current conditions. Therefore, current ratio, secondary current, accuracy class, rated burden, short-time thermal current and dynamic current should be selected together according to the switchgear design and system fault level.

Technical Data

Selection Table

The following selection table is organized for website display. Long table headings and accuracy-class cells are split into multiple lines to reduce overflow on product pages. Final parameters shall follow the approved drawing, nameplate and factory test report.

Note: Current ratio, accuracy class, rated output, short-time thermal current and rated dynamic current can be customized according to project requirements and technical agreement.

Operating Conditions

• Installation: Indoor installation for 35kV / 36kV / 40.5kV switchgear and distribution systems.
• Rated frequency: 50Hz or 60Hz.
• Ambient temperature: -5°C to +40°C reference; special service conditions can be confirmed by agreement.
• Altitude: Standard indoor service; high-altitude applications require confirmation of insulation coordination.
• Humidity: Indoor environment without severe condensation; humidity limits shall follow project requirements.
• Site condition: No severe vibration, shock or mechanical impact at the installation site.
• Air quality: Ambient air should not be significantly polluted by dust, smoke, corrosive gases, vapours or salt.
• Maintenance: Keep the resin surface clean and dry to maintain insulation performance.

Installation and Dimensions

The LZZBJ9-35/250-I / LZZB8-35Q is installed inside 35kV-class indoor switchgear or distribution cabinets. Because the 250mm code represents the cast body width, cabinet matching should focus on the product body width, primary terminal position, secondary terminal access, phase-to-ground clearance and conductor layout. The final outline drawing shall be approved before production.

Windings & Terminal Marking

The primary outlet terminals are identified as P1 and P2. Secondary winding terminals are marked according to the number of secondary outputs, such as 1S1 / 1S2 for the first secondary winding and 2S1 / 2S2 for the second secondary winding. Multi-core products may use additional terminal groups for independent measurement, metering or protection circuits.

Standards and Compliance

For international product pages, the LZZBJ9-35/250-I / LZZB8-35Q should be specified according to IEC 61869-1 and IEC 61869-2. GB-based documentation can refer to GB/T 20840.1 and GB/T 20840.2. Older catalogue references such as IEC 60044-1 and GB1208 may be retained for legacy tender compatibility, but modern documentation should use IEC 61869 and GB/T 20840 series as the preferred standard language.

Safety Notes

• Confirm voltage class, rated insulation level, current ratio, secondary current, accuracy class and rated output before installation.
• Confirm that the 250mm cast body width matches cabinet space, insulation distance and terminal access requirements.
• Check that the selected CT matches the switchgear insulation distance and system short-circuit level.
• Verify P1 / P2 polarity and secondary terminal marking before connecting meters, relays or test equipment.
• Ensure the CT is firmly fixed in the cabinet and that all primary conductor connections are tightened according to project requirements.
• Ground one point of the secondary circuit according to the switchgear grounding design.
• The CT secondary circuit must not be open-circuited while primary current is flowing.
• Before disconnecting meters, relays or test devices, short-circuit the active secondary circuit with an approved shorting device.
• Keep the epoxy resin surface clean and dry to reduce tracking and insulation risk.
• Do not use the CT in environments with severe condensation, corrosive gas, explosive atmosphere or abnormal vibration beyond design limits.
• Installation, testing and commissioning shall be performed by qualified medium-voltage electrical personnel.

Selection Guide

1. Confirm voltage level: Use this product for 35kV / 36kV / 40.5kV indoor switchgear systems.
2. Confirm cast body width: The “250” model code means 250mm epoxy casting body width, so cabinet space and insulation layout must be checked first.
3. Select current ratio: Choose the primary current according to feeder load, metering range and protection setting.
4. Choose secondary current: Select 5A for conventional meters and relays, or 1A where lower secondary burden is required.
5. Define accuracy class: Use 0.2S / 0.2 / 0.5 for metering and 5P20 / 10P10 / 10P20 or related protection classes for relay protection.
6. Check rated burden: Match the CT output with connected meters, relays, terminal blocks and secondary cable length.
7. Check short-circuit withstand: Confirm Ith and Idyn against the system fault level.
8. Approve drawings: Confirm overall dimensions, terminal arrangement, mounting base and wiring diagram before production.

FAQs