Chandrapur - Padghe

The Chandrapur-Padghe HVDC transmission system is a HVDC project in Maharashtra, India. Commissioned in 1999, this link connects the coal-fired Chandrapur Super Thermal Power Station to the major load center of Mumbai.

The converter stations were built by ABB and Bharat Heavy Electricals Limited (BHEL).

Technical Specifications

The transmission system consists of a 752-kilometer (467-mile) long bipolar overhead line. It operates at a transmission voltage of ±500 kV and has a maximum transmission capacity of 1,500 megawatts. The system is designed with overload capabilities, allowing for 1,650 MW for 2 hours and 2,200 MW for 5 seconds.

The system utilizes thyristor valves arranged in a single twelve-pulse bridge per pole. Each valve consists of 96 thyristors, each with a size of 45 cm² and a maximum voltage of 7 kV per thyristor.

Transformer Configuration

The system employs single-phase, three-winding converter transformers. Each transformer has a rated power of 300 MVA. The AC system voltage is 400 kV, while the DC voltage is nominally 500 kV.

Filtering and Reactive Power Compensation

To manage harmonics and provide reactive power compensation, the system incorporates AC filters:

Chandrapur station: 4 filter banks, each rated at 200 MVAR

Padghe station: 4 filter banks, each rated at 200 MVAR

Additionally, there are two DC filter branches per pole at each station.

Cooling System

The thyristor valves are cooled using a water-based system. This liquid cooling method, utilizing deionized water, enhances efficiency and reduces station losses.

Control and Communication

The control systems of the two converter stations required careful coordination due to their close proximity and different manufacturers. To address this challenge, a series of joint simulation studies were conducted, involving control equipment from both stations connected to a common simulator.

The primary communication method employed is Optical Fiber Communication, with Power Line Carrier Communication (PLCC) serving as a backup.

Grounding

The system utilizes a unique grounding approach. The neutral point is grounded far from the substation, connected through a 33 kV line. This design helps mitigate corrosion issues caused by high neutral currents during fault conditions.

Operating Modes

Bipolar Mode: Both conductors operate at equal currents, resulting in zero ground current. Monopolar with Ground Return: Uses one conductor (usually negative polarity) with ground return. Monopolar with Metallic Return: Employs the HVDC conductor of the faulty pole as a metallic return path.

The Chandrapur-Padghe HVDC transmission system helps to stabilize the Maharashtra grid, increasing power flow on existing 400 kV AC lines while minimizing total line losses. It enables the efficient transfer of power from the coal-rich eastern part of Maharashtra to the high-demand western region around Mumbai, addressing the geographical mismatch between power generation and consumption centers in the state.