Familiarization with the Power Thyristor Module

OBJECTIVE

To become familiar with the Power Thyristors module.

DISCUSSION

Description of the module

The Power Thyristors module consists of six power thyristors which are labeled Q₁ to Q₆. The module also contains circuitry which isolates the gate of each thyristor and protects each thyristor against current overloads. F3-1 shows the front panel of the Power Thyristor module.

Twelve banana jacks, two for each thyristor, provide access to the anode and cathode of each thyristor. This allows individual connection of each thyristor. However, two toggle switches provided to facilitate some frequently-used connections. When it is set to 1 position, the upper toggle switch (S₁) interconnects the cathodes of thyristors Q₁, Q₂ and Q₃. This switch also interconnects the anodes of thyristors Q₄, Q₅ and Q₆, when it is set to the 1 position. The lower toggle switch (S₂) connects the anodes of thyristors Q₁, Q₂ and Q₃ to the cathodes of thyristors Q₄, Q₅ and Q₆, respectively, when it is set to the 1 position.

The RESET push buttons allow the circuit breakers, which protect the thyristors against current overload, to be reset. The topmost circuit breaker is related to thyristor Q₁, the next one is related to thyristor Q₂ and so on.

The thyristor gates are connected to the FIRING CONTROL INPUTS connector through a series of internal ISOLATORS AND AMPLIFIERS. This connector can be connected to the FIRING CONTROL OUTPUTS of the Thyristor Firing Unit. It can also be connected to the CONTROL OUTPUTS of the Chopper/Inverter Control Unit.

The pin configuration of the FIRING CONTROL INPUTS connector is given in F3-1. The FIRING CONTROL INPUTS are located on pins 1 to 6 of this connector. Pin 1 is related to thyristor Q₁, pin 2 is related to thyristor Q₂ and so on. These inputs require 0-5 V level signals. Pin 7 is an input for a synchronization signal coming from the Thyristor Firing Unit (or from the Chopper/Inverter Control Unit). Pin 8 and 9 are connected to the common point of the Power Thyristor module.

 F3-1: Front panel of the Power Thyristor module.

Note that the miniature banana jacks identified FIRING CONTROL INPUT 1 to 6 are parallel connected to pins 1 to 6 of the FIRING CONTROL INPUTS connector, respectively. This allows firing control signals coming from other equipment to be used to control the thyristors.

The SYNC. OUTPUT miniature banana jack provides the synchronization signal coming from the Thyristor Firing Unit (or from the Chopper/Inverter Control Unit). This is a 0-5 V level signal which is useful to synchronize the oscilloscope when observing the firing control signals. The FIRING CONTROL INPUTS DISABLE miniature banana jack allows the internal ISOLATORS AND AMPLIFIERS to be disabled. They are disabled when a +5-V voltage is applied to this jack. The thyristors can no longer be fired in this case. The internal ISOLATORS AND AMPLIFIERS are enabled when the FIRING CONTROL INPUTS DISABLE miniature banana jack is simply left open.

The Power Thyristors module requires ac power to supply the internal ISOLATORS AND AMPLIFIERS with dc power. A 24-V ac power supply must be connected to one of the two LOW POWER INPUT jacks (they are parallel connected). The POWER ON LED lights up when the ac voltage applied to the LOW POWER INPUT jack is correct.

Using the Power Thyristor module

The Power Thyristors module can be used to build various power electronics circuits such as single- and three-phase full-wave controlled rectifiers. F3-2 and 3-3 show examples of such power electronics circuits.

In the circuit of F3-2, thyristors Q₁, Q₂, Q₄ and Q₅ are used to build a single-phase full-wave controlled rectifier. In the circuit of F3-3, the six thyristors in the Power Thyristors module form a three-phase full-wave controlled rectifier. In both circuits, the Thyristor Firing Unit provides the pulse signals required t fire the power thyristors. The power provided to the load by either one of these rectifiers can be varied by adjusting the firing angle on the Thyristor Firing Unit. Note that in both circuits, a 24-V ac power supply is connected to the LOW POWER INPUT of the Power Thyristor module to supply the internal ISOLATORS AND AMPLIFIERS with dc power.

F3-2: Single-phase full-wave controlled rectifier built using the Power Thyristors module.

The Power Thyristor module can also be also be used with the Inverter/Chopper Control Unit to build other power electronics circuits, such as a current source inverter.

 F3-3: Three-phase full-wave controlled rectifier built using the Power Thyristors module.