China
Africa
Explore chapters and articles related to this topic
Filtering and Nonlinear Protective Devices
Published in Christos Christopoulos, Principles and Techniques of Electromagnetic Compatibility, 2022
A voltage crowbar cannot be used on its own to protect sensitive circuits and it is normally necessary to control the shape and level of the voltage across the protective device after firing. This is best done by a combination of components such as the gas discharge tube and nonlinear resistor shown in Figure 11.9. This combination is referred to as a voltage clamp in that a more controlled operation is achieved. All protective devices have an inherent operational delay and hence operation is dependent on the rate of rise of the disturbance. The advantage of spark gaps is that they can conduct large currents. They are, however, slow in operation. Advanced fast-operating designs have been produced that are suitable for EMP protection.8 Solid-state devices such as thyristors may also be used as crowbar devices. Varistors (voltage-dependent resistors) of various kinds are available with fast operation and large current-handling capability and these can be used in isolation or in combination with other components for protection. The voltage current characteristic of these devices is of the form I = kvα where α is of the order of 30.
Electromagnetic compatibility/interference (EMC/EMI)
Published in Geoff Lewis, Communications Technology Handbook, 2013
Silicon controlled switches/thyristors. These are avalanche devices that operate very rapidly to provide a crowbar action. They are available in a wide range of voltages, from about 10 V to a few kilo volts. One major problem with crowbars is that the fast response can lead to a reflection of the incident energy back into the circuit.
Modelling and sizing techniques to mitigate the impacts of wind fluctuations on power networks: a review
Published in International Journal of Ambient Energy, 2022
M. V. Tejeswini, I. Jacob Raglend
A crowbar method is a safeguarding circuit against high-voltage or power surges in the power system. The crowbar circuit is used to safeguard the rotor side converter from heavy current during faults. An active crowbar allows the normal and clear operation by eliminating the short circuits when the transients are over. WTs should be in synchronism with the grid during and after the fault disturbance and provide the required amount of kinetic energy into the system during abnormal condition, as per gird code requirements. By using a crowbar, voltage controlling can be achieved during abnormal condition. In DFIG WTs the stator is connected to the grid directly. It will not be affected much for faulty condition. The rotor is connected to the grid through a power electronic converter, which is very sensitive to change in currents. Hence to safeguard the rotor side, rotor terminals are sorted via resistance. Such mechanism is known as crowbar. Active crowbars are more commonly used in DFIGs to minimise the high voltages. Usually crowbar will be connected for the fixed time scale i.e. 50 to 100ms. The peak current can happen in rotor circuit only in few cycles. Hence it is fixed to 50–100ms duration (Rubio, Soriano, and Yu 2014).
Fault-Ride through Improvement of DFIG under Symmetrical/Asymmetrical Voltage Dips
Published in Electric Power Components and Systems, 2023
Erdal Bekiroglu, Muhammed Duran Yazar
For grid-connected WECS, various protection methods are used that protect power converters and system components against overvoltage and overcurrent during grid faults. Rotor crowbar circuits are often utilized in WECS nowadays. The rotor converter is disconnected when the voltage dips, the crowbar protection circuit is connected in parallel with the rotor circuit. The crowbar circuit consists of crowbar resistors and bidirectional switches. During a fault, a new path is provided for the fault current to flow with the help of the crowbar resistor [32]. Figure 2 illustrates the suggested DFIG-based WECS with rotor crowbar that is grid-connected.