Internal sudden short‐circuit response of a new HSBDS for brushless synchronous machines tested on a 15 MVA generator

Abstract

Synchronous generators with brushless excitation have the disadvantage that the field winding is not accessible for the de-excitation of the generator. This means that, despite the proper operation of the protection system, the large deexcitation time constant may produce severe damage in the event of an internal short circuit. This paper describes a novel high speed de-excitation system (HSBDS) aimed at limiting the damage in the synchronous generator in case of an internal short circuit. The HSBDS for these generators was developed and it is in commercial operation. However in a power plant is not possible to test the operation of the HSBDS under sudden short circuit. This paper presents the results of a several tests in a laboratory 15 MVA brushless synchronous machine where internally reduced voltage sudden short-circuits have been performed. As a rated voltage short circuit could damage the laboratory 15 MVA machine, a computer model has been developed in order to assess the performance of the HSBDS in a real short circuit at rated voltage. The HSBDS under sudden short circuit conditions has been evaluated and validated through laboratory tests and computer simulations with satisfactory results.

Excitation System Technologies for Wound-Field Synchronous Machines: Survey of Solutions and Evolving Trends

“…One of the main drawbacks of the conventional brushless ESs is the difficulty of implementing the de-excitation strategies addressed in Section II. Recently, multiple tests have been carried out to provide a self-actuated high-speed deexcitation system for the conventional brushless arrangement in large power plants [50], [118]- [120]. A non-linear discharge resistor is usually bypassed in the rotor circuitry but is activated during internal short-circuits to avoid damages to the machine.…”

Impact of Synchronous Generator Deexcitation Dynamics on the Protection in Marine DC Power Distribution Networks

“…In conventional protection for AC systems, the de-excitation of a synchronous machine is considered as the loss of excitation fault and has to be protected by the generator protection system [18]. As the part of the generator protection, faster field discharging systems have been proposed in [19]- [21] and recommended in [22] to prevent machine damage from a severe fault in the vicinity of the machine or excitation system. While there are many fast discharge methods, the principal idea is to install the discharge resistor in the rotor circuit and to bypass the current flow through the resistor if the fast field discharge is needed, as shown in Fig.…”

“…It is analysed that the main focuses of [19]- [21] are limited to fast field suppression, discharge circuit topologies, discharge resistor selection and overvoltage management for brushless excitation systems. This is because brushless excitation systems have slower response (or higher time constant) compared to direct excitation systems.…”

Protection Coordination for Reliable Marine DC Power Distribution Networks

“…1, the two DC bus sections are separated first and then the fault current provided by a synchronous generator is blocked by the power supply protection (i.e., the combination of the fast action and the slow action for the bus fault). If the generator deexcitation is used for the power supply protection, the rectifier should be rigorously sized to sustain relatively high fault energy due to its slow fault blocking ability [18]- [20]. As the diode rectifier is a critical device in power supply systems, the backup protection can be considered to improve the reliability of the protection scheme.…”