25-08-2012, 12:58 PM
Automatic Voltage Regulator System
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Introduction
We are an engineering group in Business Area Power Systems – Substation Autmation of ABB Ltd, India a group company of the ABB Group of companies operates in around 100 countries. For Excitation Systems and Synchronizing devices, we are Local Engineering Centre (LEC) in India of our Product Responsible Unit (PRU), ABB Switzerland Ltd, Switzerland, who is the market leader in this business of excitation systems and voltage regulators.
The ABB group has more than 30 years of experience in the design & manufacturing of electronic voltage regulators and static excitation equipment and numerous customers all over the world are using our equipment and services to their full satisfaction.
Main Features of the Proposed System
The proposed system includes all required infrastructure for a reliable performance, such as,
• Dual Auto Channel Voltage Regulator i.e., 2 independent channels each with Auto and manual field current control mode. The Automatic mode of control includes the various limiter circuits, which prevent the machine from being operated outside the permissible operating range.
• 2 nos. of independent power converters. Each channel is provided with one no. of power converter. That is each channel controls one independent power bridge. Normally one channel is in operation with the other as hot stand by.
• Field suppression circuit preventing damage to the exciter machine in the rare event of an AVR failure.
• Hand held operator panel with LCD display for operation, programming, and parameter settings. It also displays actual signal values, and faults with fault logging up to 100 previous faults with time tagging.
• Manual control facility as an alternative to the Automatic Voltage Regulator, mainly used for service and during commissioning
MAN Control
There is a MAN control provided to be operated in case of an AUTO-channel failure (Actual value sensing failure) or for servicing purpose. In the MAN mode, the field current of the generator is controlled by means of a field current regulator. In this part of the program, the actually measured current is compared with the set point of excitation current. The difference between these two signals is applied to a PI-controller.
The changeover from the AUTO channel to the MAN control takes place in case of external command or in case of the actual value PT fault is detected. In this case the active control signal of the AVR sub-routine will be replaced by the resulting signal of the field current regulator sub-routine.
In order to ensure a smooth changeover from the AUTO to the MAN and vice-versa, an automatic follow-up control is also configured in the standard software. The non-active channel is always following the active one. This results in smooth changeover from auto to manual modes.
Power Converter
The power components are designed such that the regulator can supply a so-called field forcing for a short period of time (200% of the rated field current for 10 sec. max.). Field forcing capability contributes to a shorter setting time for the generator voltage in case of disturbances in the power network and therefore a better network support.
Scope of Supply
System components supplied with the proposed excitation system is specified in this section. The publications that are attached may mention options to the system. However, those options are only included if mentioned so in this section. Additional modules and software that are marked with (Option) are not included in the scope of supply of the AVR. They can be quoted separately.
ABB reserve their right to use components with different type and identification number without notice, provided that the system functionality and performance is maintained.