Product Overview
The LZZBJ9-12/175b/2S current transformer, also referenced as AS12/175b/2S is an indoor epoxy resin cast, fully enclosed, post-type current transformer designed for medium-voltage switchgear applications. It is used for current measurement, electric energy metering, feeder monitoring and relay protection in 10kV, 11kV and 12kV class power systems.
The 175b version is positioned as a medium-width support CT for switchgear layouts that need more terminal clearance and stronger primary-connection space than compact body designs. Its epoxy resin casting integrates insulation, mechanical support and environmental protection into one body, helping the CT maintain stable performance in indoor cabinets exposed to humidity, dust or long-term thermal cycling.
Product Type
| Item | Specification |
|---|---|
| Product name | Indoor Epoxy Resin Cast Current Transformer |
| Model series | LZZBJ9-12/175b/2S / AS12/175b/2S |
| Structure | Indoor, fully enclosed, post-type, epoxy cast-resin insulated structure |
| Voltage class | 10kV, 11kV and 12kV class medium-voltage systems |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz / 60Hz |
| Secondary current | 5A or 1A |
| Secondary structure | 2S two-secondary configuration |
| Installation | Indoor switchgear / center-mounted switchgear installation |
| Applications | Current measurement, energy metering, relay protection and feeder monitoring |
Product Display
Applications
- Indoor 12kV-class switchgear used in 10kV, 11kV and 12kV distribution networks
- Center-mounted or withdrawable switchgear requiring post-type CT installation
- Metering cabinets where one secondary circuit is used for measurement or energy metering
- Protection panels where the second secondary circuit is connected to feeder or transformer protection relays
- Retrofit projects needing a 175b body size with confirmed mounting and terminal layout
- Switchgear designs requiring optional live display device coordination
Features
- 175b medium-width body: Provides more practical space for primary terminal arrangement and busbar connection than compact-width variants.
- Epoxy resin cast insulation: The fully enclosed insulation body improves moisture resistance, surface insulation stability and mechanical protection inside switchgear.
- Two-secondary design: The 2S arrangement is suitable for combined metering and protection circuits without requiring a larger multi-core CT body.
- Reliable primary fastening: The primary conductor is tightened by bolts during installation, supporting stable contact resistance and reducing connection heating risk.
- Optional live display interface: For projects with no more than two secondary windings, a live display device can be integrated according to the cabinet scheme.
- IEC-style 12kV application: Suitable for international 10kV, 11kV and 12kV class networks using 12/42/75kV insulation coordination.
Principle
During operation, the primary current passes through the primary conductor path and establishes magnetic flux in the CT core. The secondary winding converts this magnetic flux into a standardized low-current signal for meters, relays or monitoring devices. The cast-resin body provides the required insulation distance between the medium-voltage primary side and the low-voltage secondary side.
For the 175b/2S configuration, the two secondary circuits can be assigned to different functions. One core may be used for accurate measurement or energy metering, while the other may be selected for protection duty. The rated burden, accuracy class and short-circuit withstand values must be checked together to avoid accuracy loss or protection misoperation.
Model Designation
The model code can be interpreted as follows:
| Code | Meaning |
|---|---|
| L | Current transformer |
| Z | Indoor type / post-type structure |
| Z | Epoxy resin cast insulation / fully enclosed structure |
| B | With protection level |
| J | Strengthened design |
| 9 | Design serial number |
| 12 | Maximum operating voltage / 12kV class |
| 175b | Nominal width / structure dimension code |
| 2S | Secondary schematic code / two-secondary configuration |
| AS12 | Alternative 12kV series designation for the same indoor epoxy cast-resin CT platform |
Technical Data
| Item | Specification |
|---|---|
| Rated voltage class | 10kV, 11kV and 12kV class indoor systems |
| Rated insulation level | 12/42/75kV |
| Rated frequency | 50Hz / 60Hz |
| Rated primary current | 1A to 1200A reference range according to sample data; other ratios subject to agreement |
| Rated secondary current | 5A or 1A |
| Accuracy combination | 0.2S/10P, 0.2/10P, 0.5/10P, 0.2S/0.5, 0.5/0.5 or project-specific metering/protection combinations |
| Rated output | 10VA / 20VA / 30VA reference according to current ratio, accuracy class and core configuration |
| Ambient temperature | -5°C to +40°C |
| Insulating medium | Epoxy resin |
| Installation type | Indoor support-type / switchgear installation |
| Applicable standards | GB 20840.1-2010, GB 20840.2-2014, IEC 61869-2:2012 and special project requirements |
Terminals
The 2S schematic structure indicates a two-secondary arrangement. The product may be supplied with separate secondary circuits for metering and protection. Typical terminal markings include P1 / P2 for the primary side and 1S1 / 1S2, 2S1 / 2S2 for secondary cores. Final terminal arrangement shall be confirmed according to the approved drawing and nameplate.
| Terminal Marking |
Function | Application Note |
|---|---|---|
| P1 / P2 | Primary terminals | Primary current direction and busbar connection shall follow the project wiring diagram. |
| 1S1 / 1S2 | First secondary core | Usually used for metering, measurement or the first specified secondary circuit. |
| 2S1 / 2S2 | Second secondary core | Usually used for relay protection or additional monitoring circuit. |
| Live display terminal | Optional voltage indication device | Available when the secondary winding quantity is two or less and the project requires live display indication. |
Selection Table
The following table is arranged by rated primary current range and common metering/protection configurations. Long accuracy and output data are wrapped into multiple lines to improve readability on website pages and mobile layouts.
| Rated
Primary Current (A) |
Accuracy
Class Combination |
Rated
Output(VA) |
Short-Time
Thermal Current |
Rated
Dynamic Current (kA) |
|---|---|---|---|---|
| 1 | 0.2S / 10P 0.2 / 10P 0.5 / 10P 0.2S / 0.5 0.5 / 0.5 |
10 / 20 10 / 30 20 / 20 |
1.0kA | 2.5 |
| 10 | 5kA | 12.5 | ||
| 20 | 10kA | 25 | ||
| 30 | 12kA | 30 | ||
| 40 | 16kA | 40 | ||
| 50 | 10 / 20 10 / 30 20 / 20 20 / 30 |
18kA | 45 | |
| 60 | 20kA | 50 | ||
| 75 | 31.5kA | 80 | ||
| 100 | 45kA | 112.5 | ||
| 150–300 | 45kA | 112.5 | ||
| 400–600 | 63kA | 150 | ||
| 800–1200 | 80kA | 180 |
Note: The above values are for technical selection reference. If project requirements exceed the listed range, final parameters shall be confirmed by agreement between manufacturer and purchaser. Nameplate data, approved drawings and factory test reports shall prevail.
Structure Reference
| Structure | Application Reference |
Selection Note |
|---|---|---|
| 175b | Medium-width support structure | Suitable for switchgear layouts requiring stronger body support and larger internal clearance than compact 150b designs. |
| 2S | Two-secondary schematic arrangement | Used for metering/protection or dual-secondary requirements. |
| Live display option | Optional device integration | Can be added when the secondary winding quantity is two or less and the project requires voltage indication. |
Service Conditions
- Installation location: indoor medium-voltage switchgear
- System voltage: 10kV, 11kV and 12kV class networks
- Rated frequency: 50Hz / 60Hz
- Ambient temperature: -5°C to +40°C
- The installation environment should be free from severe vibration, conductive dust, corrosive gas, explosive medium, heavy pollution and abnormal condensation.
- For high altitude, humid, coastal, high-pollution or special switchgear conditions, technical confirmation is required before ordering.
Standards and Compliance
The LZZBJ9-12/175b/2S current transformer can be supplied according to GB 20840.1-2010, GB 20840.2-2014, IEC 61869-2:2012 and special project requirements. Routine tests typically include ratio test, polarity verification, accuracy test, dielectric withstand test, insulation inspection and appearance inspection. Additional project-specific test documents can be confirmed according to the technical agreement.
Installation and Dimensions
The product adopts an indoor support-type structure with top primary terminals and lower secondary terminal arrangement. The 175b structure shall be selected according to switchgear mounting space, terminal direction, busbar clearance and secondary terminal access. The approved drawing shall be used before switchgear production or replacement.
Dimensions
| Item | Dimension / Note |
|---|---|
| Structure code | 175b support-type design |
| Secondary schematic | 2S two-secondary arrangement |
| Primary terminal arrangement | Confirmed according to current ratio and approved drawing |
| Secondary terminal arrangement | Terminal box / lower terminal block according to drawing |
| Mounting holes | Confirmed according to outline drawing |
| Drawing confirmation | Required before switchgear production or replacement |
Safety Notes
- Confirm model, current ratio, secondary current, accuracy combination, rated output and insulation level before installation.
- Check mounting space, busbar connection, primary terminal position, secondary terminal layout and phase clearance before assembly.
- Tighten the primary bolts properly during installation to ensure reliable electrical contact.
- Use the approved drawing for the selected 175b/2S structure and terminal arrangement.
- Connect P1/P2 and secondary terminals according to polarity markings and the project wiring diagram.
- The secondary circuit of a current transformer must not be open-circuited when the primary circuit is energized.
- Before disconnecting meters or relays, short-circuit the secondary circuit through an approved shorting terminal block.
Ordering Info
- Product model: LZZBJ9-12/175b/2S or AS12/175b/2S
- Rated primary current and rated secondary current
- Accuracy class combination and rated output for each secondary core
- Rated insulation level and applicable standard
- Required short-time thermal current and dynamic current
- Secondary core quantity, schematic code and terminal marking requirement
- Live display device requirement if needed
- Switchgear layout, mounting dimensions and primary terminal direction
- Quantity, certificates, routine test reports, labeling and packaging requirements
Selection Guide
- Confirm naming: Use LZZBJ9-12/175b/2S or AS12/175b/2S according to the project document, drawing and nameplate requirement.
- Check cabinet fit: Verify whether the 175b body size matches the switchgear depth, busbar position and secondary terminal access.
- Define two secondary circuits: Assign each secondary core clearly, such as measurement + protection or metering + protection.
- Select ratio and burden: Match the primary current, secondary current and rated burden with the connected instruments, relays and cable length.
- Confirm protection duty: Check protection accuracy class and short-circuit withstand level against relay setting and switchgear fault current.
- Review live display need: Confirm whether the optional live display device is required and whether it is compatible with the selected two-secondary arrangement.
- Approve drawing first: Confirm primary terminal spacing, mounting holes, terminal box position and polarity markings before production.