Progressive Fault Isolation and Grid Restoration Strategy for MTDC Networks

Abstract

A multiterminal dc (MTDC) grid has a number of advantages over traditional ac transmission. However, dc protection is still one of the main technical issues holding back the expansion of point-to-point dc links to MTDC networks. Most dc protection strategies are based on dc circuit breakers; however, DCCBs are still under development and their arrival to the market will come at an unclear time and cost. Conversely, ac circuit breakers (ACCBs) are readily available and represent a more economic alternative to protect dc networks. Following this line, a protection strategy for MTDC grids is proposed in this paper. This uses ACCBs for dc fault current clearing and fast dc disconnectors for fault isolation. The faulty link is correctly discriminated and isolated while communication links are not required. This strategy contributes to a reduced network outage period as the nonfaulty links are out of operation for a relatively short period of time and are restored in a progressive manner. The effectiveness of the proposed strategy is tested in PSCAD/EMTDC for pole-to-ground and pole-to-pole faults.

Coordination of MMCs With Hybrid DC Circuit Breakers for HVDC Grid Protection

“…The ACCBs then open, taking about 50 ms. As a result, the fault current naturally decays to zero and all FDs open. This process takes a very long time (e.g., 200 ms) [7]. The ACCBs can then re-close, followed by the de-blocking of MMCs and re-closing of FDs at the healthy circuits.…”

“…The deployment of HVDC grids and their reliable operation will depend on the adequate performance of their protection schemes during dc faults. This is challenging as a dc network has a lower inductance than an ac system of equivalent rating and, thus, exhibits a higher rate of change in fault currents and a faster fault propagation [7]. A dc grid protection system should have the ability to interrupt fault currents when their magnitude is low not only to prevent damaging power system equipment, but also to bring down the rating and, hence, the cost of protection devices such as dc circuit breakers (DCCBs).…”

Enhanced Control of Offshore Wind Farms Connected to MTDC Network Using Partially Selective DC Fault Protection

“…In [13], a DC fault protection method that uses AC circuit breakers (ACCBs) and fast DC dis-connectors to isolate DC fault and facilitates system restoration is proposed. This method sacrifices DC grid continued operation in favor of post-fault operation that prioritizes reduction of the outages and partial system restoration by deliberate separation of healthy parts of the DC from the faulty part.…”

“…Also, it has provided extensive guidelines for recovery sequences of grid following and forming converters, covering a range of actions, including converter de-blocking and ACCB reclosing. However, the approaches in [13,14] lead to brief shut down of the whole DC grid following fault inception and take relatively long period to interrupt DC fault currents and to isolate the faulty line.…”

Fault tolerance and protective schemes for DC power distribution

“…The DC fault does not have a natural zero current crossing so that the arc can be extinguished when the AC breaker opens. One method of using the AC breaker for DC fault protection is to locate the AC breaker at the AC side of the power converter, and a DC switch at the power converter DC end to interrupt the DC fault [18][19][20]. The AC circuit breaker trips the fault current first, and the DC switch activates once it has fallen smaller than the threshold magnitude.…”