Switchgear Control Apparatus Surge Voltage Suppression
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Solution Overview
Problem
Conventional switchgear control techniques are ineffective in suppressing surge voltage during the reconnection of unloaded power lines without a special voltage sensor system, as they rely on detecting residual DC voltage, which is not typically available in standard power systems.
Innovation Solution
A switchgear control apparatus that includes a voltage sensor for detecting AC voltage, a current transformer for detecting main circuit current, a contact opening time sensor, an interruption time sensor, and a reclosing time decider to determine the optimal reclosing time for the circuit breaker based on AC voltage, main circuit current, and contact opening time, eliminating the need for a special voltage sensor system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a special voltage sensor system (capacitive voltage divider) is used to detect residual DC voltage, then measurement precision of residual voltage is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses a current transformer to detect the current waveform, which serves as a copy or indicator of the voltage state. By analyzing the current waveform characteristics (zero-crossing points, amplitude), the system indirectly determines the voltage phase and residual charge state without directly measuring voltage, thus avoiding the need for complex voltage sensor systems.
Solution Approach 2:
The patent replaces the electrical measurement approach (voltage sensing) with an electromagnetic induction approach (current transformation). The current transformer uses electromagnetic induction to detect current, and this current information is then processed to infer voltage phase, substituting a simpler electromagnetic measurement system for a complex direct voltage measurement system.
2Reliability
If conventional control technique using capacitive voltage divider is applied, then surge voltage suppression capability is improved, but ease of operation and practicality deteriorate
Solution Approach 1:
The system uses current waveform as a copy of voltage information. By detecting current zero-crossing points and analyzing current amplitude variations, the system infers the voltage phase and timing without direct voltage measurement, making the control technique practical for standard power systems.
Solution Approach 2:
The current transformer and control system use the existing current flow in the circuit to provide the necessary information for reclosing control. The current waveform itself contains the timing and phase information needed, eliminating the need for separate specialized sensing systems.
3Device complexity
If standard voltage sensor system is used without DC voltage detection capability, then device complexity is reduced, but measurement precision of residual DC voltage deteriorates
Solution Approach 1:
The patent uses current waveform characteristics as a copy or proxy for voltage information. The current transformer output provides a simplified representation that contains sufficient information (zero-crossing timing, amplitude variations) to determine the optimal reclosing point without directly measuring the complex residual DC voltage.
Solution Approach 2:
The current transformer acts as an intermediary between the power circuit and the control system. It transforms the hard-to-measure voltage information into easily detectable current signals, which then serve as the basis for determining reclosing timing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively suppresses surge voltage during the reconnection of unloaded power lines by determining the reclosing time based on AC voltage and current data, ensuring reliable power system operation without requiring a special voltage sensor system.
Implementation Method 1
a voltage sensor for detecting an AC voltage on a power source side of the circuit breaker
Implementation Method 2
a current transformer for detecting a main circuit current flowing through the circuit breaker
Data Source
AI summary
A switchgear control apparatus includes a zero point interval detecting circuit, an interruption time judgment circuit and a reclosing time decision circuit. The zero point interval detecting circuit detects time intervals between successive zero points of a main circuit current. The interruption time judgment circuit judges that interruption time of the main circuit current is time of a zero point immediately preceding a zero point at which a difference between the time interval between two successive zero points and half the period of a commercial AC voltage exceeds a specific value. Upon detecting the gradient of the main circuit current at the interruption time, the reclosing time decision circuit sets reclosing time at a point in phase where the AC voltage has a maximum negative value if the gradient is positive, and at a point in phase where the AC voltage has a maximum positive value if the gradient is negative.