Distance protection zone 3 misoperation during system wide cascading events: The problem and a survey of solutions

Highlights

• Setting of a distance relay according to NERC standards is illustrated on a test system.

• The aforementioned test system is used to illustrate the problem of zone 3 distance protection misoperation.

• Solutions to the problem of distance protection misoperation in literature are reviewed and organized into three main categories.

• The methods in each category are briefly explained.

• The pros and cons of each method are also summarized.

Abstract

Distance relay zone 3 misoperation has been responsible for major blackouts around the world. Zone 3 misoperation generally occurs under system wide cascading events such as the 2003 Northeastern US–Canada blackout or under stressed system conditions such as the 2015 Turkish blackout. This paper explains the problem of zone 3 distance protection misoperation. The paper then proceeds to survey the literature for possible solutions to increase distance relay security to prevent distance protection misoperation. Three categories of solutions were proposed in literature to address the problem of zone 3 distance protection misoperation. The first one is anticipation and prevention of misoperation in the planning stage. The second one is communication assisted protection schemes that use remote measurements to enhance relay security. The last one uses local data to enhance distance relay security.

Introduction

With the deregulated market structure in the United States and Europe, grid operators are under more pressure to reap more profits of existing infrastructure due to increased competition. The grid is thus increasingly operated near the threshold of stability. Failure of the grid, better known as blackouts, carries catastrophic economic and societal sequences. Large blackouts tend to be due to either extreme natural events such as hurricanes or a series of events called cascading failures [1]. In this paper, we only focus on cascading events. Those events can be any of the following: line tripping, overloading of other lines, malfunctions of protection systems, power oscillations and voltage instability [2]. The reason that is considered in this paper is distance protection misoperation which is a contributing factor in seventy percent of all cascading events [3]. If not discovered and mitigated in an early stage, cascading events generally lead to a complete blackout. With today's society much dependence on electricity as a form of energy, preventing such damage is of high importance.

Cascading failures are defined as “a sequence of dependent failures of individual components that successively weaken the power system” [4]. Since the 2003 US–Canada blackout, cascading events have drawn much attention in the industrial and academic community. Even though the world has witnessed many blackouts prior to the 2003 blackout [1], the dramatic causes and consequences of the 2003 blackout have left industrial and academic community with the burden of exploring this phenomenon in more detail. To understand the severity of the 2003 blackout [5], it sufficient to say it had caused the loss of 62 GW which caused the lights to turn off for more than 51 million people in the eastern interconnection. Considering the many components and the bits and pieces involved, a domino effect of events evolved slowly (hours) or fast (seconds) according to the region causing a degradation of the integrity of the system leading ultimately to a complete blackout. The main reason of the 2003 blackout was distance relay misoperation. Daunting efforts had to be exerted to gain more knowledge and understanding of the underlying phenomenon.

Relays by design act quickly to remove the fault from the system by disconnecting faulted lines. However, sometimes relays fail to perform such function which is considered a protection system misoperation. Of all protection system misoperations that lead to cascading events, this paper focuses exclusively on distance protection misoperation. A protection system misoperation is defined as “a failure to operate as intended for protection purposes” [6]. Various categories are given for misoperation in [6]. However, in this paper the word misoperation will be used exclusively to mean only one of them, namely, an operation in which a protection system trips a healthy line due to heavy loading when no fault exists. In other words, other causes of distance protection misoperation such as power swing are not considered in this paper. Notable cascading events [2], [7] begin with lines that were tripped due to actual faults. The tripping of those faulty line causes the current flowing in those lines to be redistributed to adjacent lines. Those lines may be overloaded and thus tripped incorrectly – protection misoperation – which may trigger a sequence of cascading events that might ultimately lead to a blackout. It should be noted that regardless of the initial triggering events – whether a fault or not – that cause cascading events, historically those cascading events were triggered under stressful system conditions [5], [8].

As mentioned in [2], one of the effective ways to prevent cascading events is to specify potential undesirable relay operations ahead of time. In this paper, we show that even though distance protection misoperation can be anticipated ahead of time, prevention of this misoperation is not possible with distance protection principle only because the distance protection principle is not able to be selective in some regions of its operation.

The paper is organized as follows: Section 2 provides a sample distance relay that is set according to NERC standards. Once this relay is set according to NERC directives, it will be explained in the same section that the relay may still misoperate under various operating conditions. Anticipation and detection of distance relay misoperation in the planning stage is described Section 3. Section 4 provides an overview of the communication assisted schemes that have been proposed to eliminate the distance protection misoperation. Lastly, Section 5 offers a survey on the methods that were suggested in literature to enhance the distance protection security using local data only.