Electronic Current Transformer (ECT) Solution:​​ ​Economically Driven Retrofit

I. Pain Points: Challenges in Conventional Substation Retrofit
Traditional electromagnetic current transformers (CTs) present numerous issues in aging substations:

• High Retrofit Cost: Replacing conventional CTs requires large-scale power outages, civil construction, and updates to protection panels, cabling, and grounding systems. Combined costs exceed 50%.

• Poor Compatibility: New devices have interface mismatches with legacy secondary systems (e.g., relays, meters), necessitating additional conversion devices.

• Space Constraints: Aging substations have limited space. Conventional CTs are bulky and heavy, making hoisting difficult and potentially requiring foundation expansion.

• Lengthy Commissioning: Retrofits involve multi-system integration testing. Tight outage windows delay grid restoration.

II. Solution: ECT (Electronic Current Transformer) Economical Retrofit
Achieve an upgrade path of "minimizing retrofit cost, maximizing compatibility with existing systems" through ECT technology:

**▶ Core Economic Advantage: Significant Reduction in Comprehensive Retrofit Cost**

**▶ Compatibility Design: Seamless Integration with Existing Infrastructure**

1. Hybrid Interface Output:
   ECTs feature built-in Analog Output (4-20mA/0-5V) + Digital Output (IEC 61850-9-2), compatible with three scenarios:

• Legacy Protection Devices: Connect directly to existing current input terminals.

• Digital Protection Systems: Send GOOSE messages via Merging Units (MUs).

• Metering Systems: Simultaneously output analog signals for meter sampling.

2. Plug-and-Play Installation:

• No Crane Required: ECT weight <15kg (vs. ~150kg for conventional CTs), enabling manual installation.

• Compact Size: Diameter &le;200mm, fits original CT mounting brackets.

• Flexible Rogowski Coil: Can be wrapped around existing primary conductors, eliminating busbar disassembly.

3. Adaptive Power Supply Scheme:

• Laser Power Supply: Energy delivered via fiber optics embedded in insulators, eliminating separate power supplies.

• Busbar Power Harvesting: Inductive power harvesting uses primary current for self-supply, suitable for passive environments.

III. Value Realization: Rapid Return on Retrofit Investment

IV. Representative Case Study: 110kV Gudu Substation Retrofit

• Original Configuration: Electromagnetic CTs (Commissioned 1985)

• Retrofit Solution:
  Installed 12 ECTs (Class &plusmn;0.5S) to replace conventional CTs. Output signals:
  &rarr; 4-20mA fed into existing relay protection devices.
  &rarr; IEC 61850-9-2LE fed into newly installed smart control cabinets.

• Economic Results:

• Total Investment Reduced by 42% (Primarily saved on cabling, civil works, commissioning).

• Outage Time Reduced from originally planned 7 days to 2.5 days.

• Compatibility Verified: Conventional differential protection operating time maintained at 15ms, with no failure to trip / maloperation.

V. Why Choose the ECT Economical Retrofit?

1. Controlled Cost: Retrofit budget reduced by 30%-50%, ROI < 3 years.

2. Risk Mitigation: Maintains existing protection logic, avoiding system reconfiguration risks.

3. Smooth Evolution: Compatible with today's analog systems, supporting tomorrow's digital grid.

4. Emergency Replacement: Faulty CT replacement completed in as little as 48 hours.