Digital Static Excitation & Control system for 500KW to 200MW SynchronousMachine

DIGITAL STATIC EXCITATION SYSTEM(Rotary) being offered is intended for providing excitation power supply directly to the main field (Exciter field in case of Rotary) of alternator through the slip rings. The excitation system is built around the state of the art digital excitation control system. The digital controller provides all necessary controls, limiters and protection (related to excitation) to enable the alternator run in solo, parallel and grid parallel modes. The output of the controller +10V DC is fed to the 6 pulse firing card designed and manufactured by Amtech. The firing card generates firing pulses for all the six thyristors employed in the power circuit. The power circuit consists of six nos. of power thyristors, configured from a 3 phase bridge, mounted on massive heat sinks and interconnected by bus bars. The thyristors are rated to have sufficient voltage and current margins in order to ensure high reliability. The power circuit is force cooled by a high power System mounted fan, in order to keep the heat sinks cool.

The power output voltage of the thyristor bridge will go both positive and negative. The negative field output will help alternator to recover fast after a load throw off. The power input to the bridge will be the secondary voltage of a 3 phase excitation transformer. The secondary voltage will be rated to give adequate field forcing required for transfer conditions. Power input is applied through a power contactor. A crow bar circuit is provided across the main field to contain any induced over voltage. The crow bar is also turned ON under excitation OFF conditions. The resistor box provided in series with the crow bar will be designed to dissipate stored energy of the main field. The firing circuit employed is capable of providing firing pulses from residual voltage of the alternator. However, a separate field flashing circuit is provided to boost the residual voltage in order to enable firing circuit to put out firing pulses for the thyristor bridge. A dedicated high energy surge suppressor is provided in the system which will be connected directly across the main field or power output. This will protect the bridge thyristors and the insulation of the main field.

We manufacture Digital Static Excitation System. It is offered in various types like single controller single power circuit, Single controller redundant power circuit, Dual Controller Dual Power circuit, Dual Controller single power circuit.

Digital Firing Card

The control board PCA-2005/B is a multipurpose board and specifically designed to meet the high-end performance of the power electronics products like AC Power Controller, Control Rectifier, Soft starter etc…

It uses 32-bit High-Performance Digital Signal Processor. The control board generates the necessary firing pulses for all 6 Thyristors. It accepts various inputs from different control circuits, line voltages and digital operation System (LCD keypad) to generate the necessary control and firing signals. It handles the user interfaces and core algorithm and generates Thyristor firing signals.

Thyristors Stack

We are manufacturing up 10000Adc thyristor stacks with fast acting fuse protection and temperature protection their performance is proven in the Indian weather.

Crowbar Operations

Critical to the operation of the crowbar power switch is reliable control of the trigger circuits that turn the crowbar power switch on. The crowbar power switch thyristors must be triggered such that sustained over voltage of the machine field is prevented, yet triggering must not occur under any condition where the six- SCR bridge is expected to continue operating and not shut down. It must be ensured that the current path to the power switch is the only one available to field current during excitation system shutdown.

The crowbar consists of two anti parallel thyristor TH1 and TH2 connected across the excitation field circuit of alternator. Each crowbar control triggers the associated SCR under the following conditions. Only one section is triggered at any given time, dependent upon the field voltage polarity at that time. Other section triggers the SCR when SCR anode-to-cathode voltage (equal to field voltage prior to triggering) is positive and exceeds a factory-preset level (set by the trip level Adjust for that section). The forward section can be enabled to trigger at any SCR anode-to-cathode voltage level sufficient to fully energize the power supply for that section.

The forward section is enabled by closing the external contact connected to the Crowbar External Trigger input. This results in triggering at a much lower voltage than the trip level. This method of triggering is used during normal shutdown of the excitation system, providing as alternate, resistive path for field current to freewheel and dissipate the stored energy in the machine field.

The total response time from the detection of fault to firing of crowbar thyristor varies from 50 μs to 150 μs depending upon the instant at which gate driver circuit fires in clock synchronization of timer circuit IC U13.