Chapter 10 impedance relaying distance relays or double actuating quantity relays with one coil the restraining coil energized by voltage which by virtue of the fact that is connected to a PT or a vt is proportional to the line voltage at the relay location. The other coil the operating coil is energized by current again proportional due to the fact is connected to a CT to the line current at the relay location. The torque to operate the relay may be described by the fraction I over V or the current over the voltage. As the current increases, the relay will tend to operate as the voltage increases the relay will tend to restrain now, I over V which of course tomes law is equal to one over Zed, where Zed is the impedance of the circuit which is drawing the current AI driven by the voltage V. In this case, the voltage to operate the relay is governed by the current feeding the fault on the line.

The limiting factor on the amount of fault current flowing for a given line voltage is the impedance of the line the closer to the station The fault is the less line impedance, the higher the fault current is and the greater operation torque on the relay. In fact, assuming that the impedance of the line is uniform the impedance measured to the fault is proportional to the distance to the fault has such protection is called impedance protection or distance protection. The protected zone is not exact, but it's good Enough to provide adequate high speed protection especially when combined with multiple zones and high speed end to end communication signaling. Also one of the problems with this simplistic setup as described here the relay does not know what direction that the current is flowing. It operates solely on the magnitude of the current normal operate for faults in the opposite direction looking back into the bus, this is called the characteristics of a relay, which can be altered to give more favorable results as we shall see.

Distance protection is a very widely used protection scheme in transmission lines. The RX diagram is useful in plotting the characteristics of distance relays. Remember that reactance is plotted vertically and resistance is plotted horizontally. Any resistance is represented by a vector of magnitude Zed at a set angle we'll call it theta from the vertical axis, the three variables voltage current and the phase angle between them can be converted and plotted on an RX diagram because V over i is equal to Zed and if you complied said then you can plot V over i. impedance said is defined as the ratio of RMS value of voltage and Zed is equal to V over I which is equal to resistance plus reactance. And they can be plotted on an RX diagram. Our remember is As the impedance said times cosine of the angle x is equal to the impedance times the sine of that angle.

Theta is positive. If I liked the animation its negative, if I leads the das V and I can be converted on an RX diagram as shown here. The family of impedance relays or distance release can offer a wide range of characteristics which we're about to look at. relays which measure plane impedance Zed, are called impedance relays. The characteristics on an RX plane is a circle with a center at the origin and a radius as Zed relays which measure impedance Respond to faults on one direction only are called directional impedance relays. The characteristic of this circle here is not a directional relay, it'll operate for any impedance inside the circle as we will see in the next slide.

The impedance really operating characteristics is a circle represented on our x diagram operations. In other words when the relay picks up, it will pick up for any combination of voltage and current V over I or the impedance on a on this RX diagram that falls inside the shaded area. The relay will pick up anything that is the voltage ratio of V over I that falls outside the circle. The relay will restraint So, the characteristics that we say the relay is a circle with a center at the origin on an RX diagram and any impedance measured inside that circle will operate the relay. Now, if we plot a line on the RX diagram, it will look like this as the line extends down to the other end, it will produce a straight line on the RX diagram, starting at the origin and extending upwards to the right.

So, any fault along the line should operate the impedance relay because of the characteristics of the relay. There are some disadvantages to this relay. This really definitely will pick will protect that line however, This relay, as you can see is non directional. In other words, it can look in the other direction, towards the bus and out other lines. So it is not a completely exclusive type relay, it will trip for faults on the line. Unfortunately, it will trip for other faults that are not on the line.

In other words, it responds to faults on both sides of the CP and the VTX. And it can't discriminate between internal and external faults readily for all cases. And it's also affected by the resistance of the fault itself. So the line does a extend as a straight line. But if we add the impedance of the fault, say it's an arc fault or a tree, then that has to be added to the impedance and it could very well fall Outside the protected zone and the relay may not operate. It is also very sensitive to power swings as a large areas covered in the circle of the RX plane as the system goes through a power swing which would happen during say storm conditions, the relay has a tendency tendency to be very sensitive and it could operate.

In order to mitigate these problems, the mole type distance relay was developed also known as admit the admittance relay and sometimes it's even called an angle impedance relay. Through various techniques, the mole relay characteristics shifts the impedance of the circle on the RX dial Round along the line for which it is being approached as protecting now in the old school days and there's still a lot of these relays out in the system such as the KT four and the KT relay, the Westinghouse kt relay. This shifting was done using various magnetic and capacitive effects inside the trench or the relay itself. In the more modern relays, they can change the characteristics with mathematical algorithms because it is a digital relay, and they have the luxury of doing that. However, the mo characteristic is very convenient because it doesn't, isn't just restricted to the narrow impedance of the line, which may prevent it from tripping if it was to if the character was too narrow by providing a circle with a maximum torque, and we'll talk about that in a few minutes along the line, this tends to give a really good coverage of the line, especially if we're talking about multiple zones and communications end to end so that you can differentiate for internal and external folks.

However, we're going to talk about the motor relay, and then we'll look at the KD relay. And then we'll have a quick look at some of the more modern IED relays that can actually change the characteristics quite drastically from the actual mobile relay itself. For now, let's assume that the characteristic of the relay in this case has been shifted from the origin. So that it is passing through the circle passes through the origin and the diameter is actually the diameter of the Line the characteristic is directional. Now it will operate for faults in only one direction. Or we should say, along the line or in the vicinity of the line, it doesn't react to false in the opposite direction.

So this is a very improved characteristic of the line. The operating torque is dependent on where inside the fault inside the circle the fault occurs with a maximum torque being at the very point as to where the line crosses a circle on the other away from the origin. More real usually have multiple characteristics that simultaneously measure the impedances in in the system and along the line. In most cases, one element is set to reach 80% of the line and this is called zone one. A second element is set up to reach 120% of the line and this is called zone two. Another element is set to reach in the opposite direction and it is called zone three.

Now, all of these zones are used to feed into tripping logic, and some of them are permissive overreach. Some are called permissive under each some of them are called directional comparison But the fact that you've got three zones now, you can switch the logic after the fact that they've done their measurement and either picked up or not picked up in order to protect the line and we'll see that in subsequent slides as we go along. The important thing to note here is that one really can have several zones and those zones, characteristics can be various sizes, length and directional measurement. Let's talk about zones of protection. Now. A common practice is to divide the power system up into zones or the line up into zones if you would for protection purposes.

If a fault occurs anywhere within the zone asst components within that zone will work to isolate the fall the fault in a certain way. A zone is defined as the area from a current transformer on the line that is connected to one particular distance relay and it is extended the zone is extended out to a defined reach along the line, it could be 80% 90% or 120% or any of the in between fractions as well. In transmission line protection, it is common to use an under reaching zone, call it zone one and an overreaching zone, zone two. A third zone, as we mentioned before is also used in the reverse direction, but we're not going to look at that right now. We'll look at it a little bit later. showing here is an example of to define zones of protection on the line.

Protected by relay a. And you can see it here that it is bound by the location of the C t that is connected to relay a at station A. and it extends out around 80% or 90% of the line and we call that zone one. Zone two can be also defined the area that is protecting is 120% of the line iterates from boss a where the CT is connected to relay a and extends out along the line and will reach past the second station because it's reaching 120% of the line. So we defined these two zones as zones of protection. The relay relay with operate for zone one and zone two. What we do with those operations after the fact is the logic that we're going to talk about later.

But for now, we're just going to define those zones and that the relay will operate in those particular zones. The same setup is working on the other end of the line at the other station. The zones of protection there are defined by the CT that is connected to relay B, and it has two zones of operation as well, which reach 80 to 90% for zone one, going in the opposite direction and zone two 120% which reach reaches into the other station of course, in a similar fashion So far we've only discussed the fact that the impedance release is looking at the line and it actually has two zones of protection to call it zone one and zone two protection zone one protects or looks at only a part of the lines, zone two looks at more than 100% of the line. What we do afterwards with the logical tripping sequences is what characterizes the various types of relay protection that you will employ to protect a line.

So let's look at what they call permissive overreach transfer trip or p. Ott. Zed one is still looking at 80 to 90% Have the line impedance it under reaches the remote end, but does not have any time delay. So we're going to set it tripping sequence to trip without any time delay or instantaneously for any fault within its own protection which is zone one, which covers 80 to 90% of the line. Zone two is set to protect 120% of the transmission line. So two covers all of the line, including zone ones reach and overreaches, their mode and a time delay of 15 to 30 cycles or 250 to 500 milliseconds is set to initiate a trip if a fault is detected anywhere within It's so this tripping logic is set up for the other end as well. So you have really be looking in the other direction, it has zone one it has zone two, zone one is set to trip instantaneously.

Zone two has a delay trip of 250 to 500 milliseconds. The protection zones for relay A and B start from bus A and B respectively. Two zones of protection have been defined for each relay zone one zone two. So, one is set to protect 80 to 90% of the transmission line and zone two is set to protect 120% of the transmission line relay looks forward to bus B and relay B looks forward to bus The circuit breakers one and two are governed by relay a and relay B respectively. So you have this functionality where you have two zones of protection looking at the line, one zone is instantaneous, the other has a time delay. In our simple setup here, I've said that circuit breakers one and two are governed by relays A and B respectively, which means that each end looks after tripping its own hand and protecting the line by doing this.

Let's assume for a moment that zone one protection at the bn is removed. Let's say something's wrong, it doesn't work. What I've just removed it from the The logic here. So we have two zone tubes looking at the line plus zone one looking at the line from the relay a. If we apply a fault or if a fault were to exist or happen at this point on the line, both zone two's will see default and clear it in 500 milliseconds. I've diagrammed the logic here and I've exaggerated the time delay of course, just for clarity purposes, you can see that zone two will initiate a timer.

The timer will then go and permit the breaker to trip after 500 milliseconds at each of the respective ends. In systems of ever increasing transmission voltage 250 k v3 45 507 35 kV etc, it becomes imperative that the faults are cleared even faster in zone two In fact, we'd like them to trip almost instantaneously. Instantaneous clearing of zone two can be accomplished with the help of high speed communication links, such as a microwave, transmitter and receiver at both ends. Let's have a look at how that will work. permissive overreach transfer tripping employees high speed and and communications permissive overreach transfer tripping is a specialized protection scheme used to provide high speed tripping for faults anywhere along a high voltage transmission line. In the permissive overreach, scheme, communication and Intelligence is use between the two terminal stations in order to determine the location of the system fault.

As you can see from the diagram, the logic at each end now includes a transmit function TX as well as the receive function RX. Each zone will still initiate a 400 millisecond delay trip at their respective ends. However, the 400 millisecond time delay is bypassed and trips at high speed if a permissive tone is received from the other end. Let's have a look at how that works. Let's apply a fault FL one on the line in between station a and station B. But just beyond station AES zone one protection Remember now we have removed zone one from station B just so we can see how this permissive zone two protection works at a, the under reaching zone one relay does not see the fault and therefore does not operate.

The overreaching zone two relays at both station A and B will see the fault and the only issue they will initiate three things. One, they will begin the timer as before and that will trip the local breakers after 400 milliseconds. However, each relay will also operate to key a transmitter TX to send it permissive tone to the other station. Both stations will initiate instantaneous local tripping that will happen only if after receiving a permissive tone from the other station. Therefore, the overreaching zone two relays at each station anb will bypass the 400 millisecond time delay to trip its local line terminal breakers at high speed via permissive receive signal are acts as a result system fault FL one on our high voltage line l one is cleared at high speed or you might say it's cleared instantaneously. So, you can see that even though it's only zone two faults being sensed at either end, we still get instantaneous or high speed tripping due to the communication back and forth from one end to the other.

If we apply a fault this time at FL to which is beyond the remote station be the under reaching On one relaying at station a does not see the fault and will not operate. The more sensitive overreaching zone to relay however, will see the external fault and will operate. Station a will not trip instantaneous instantaneously as the permissive receive tone RX has not received from station B relay. The station B relaying does not key that TX permissive send transmitter because it will not detect the fault as it is located behind terminal at station B. As a result, the instantaneous tripping of station a does not occur as for the external fault, FL to thus in a permissive, overreach, overreaching scheme it is possible to have high speed tripping at 100% protection coverage for All internal faults and not over trip for external faults. In directional comparison protection, an added step of security is added to the system in that for faults that are outside our system of protection, we want to ensure that the line will a lot trip high speed.

So we send out a blockings signal. And you can see we've added zone three logic to our tripping system here, whereas zone three will actually open the instantaneous tripping of the line for permissive overreach. If the fault is in zone three We do not want the line to trip. If the fault is in zone three, we certainly don't want it to trip instantaneously anyway. The directional comparison scheme incorporates as I said a third zone of protection and a second transmitted signal. As in the permissive overreach scheme, we have two zones of protection zone one which covers 80% of the lines zone two which covers under 25% of the line, station a distance relay look into the direction towards station B and station B distance relay looks towards station a.

Both terminal stations have a third zone zone three which look in the opposite directions. There is a third element of the distance really that operates for faults behind the terminal station, as in the permissive overreaching scheme committee. occation intelligence between the local and the remote station is employed to communicate the location of the system fault. In this protection scheme, the blocking tone, which is indicated in green is sent to the other station. In the event the external fault occurs behind the terminal. The Zone three faulty detecting relays operate for faults in the opposite direction of the protected line to key a transmit transmitter equipment which block zone to high speed output via the block receive RX contacts.

This will re assure no instantaneous tripping for a fault outside the zone of protection. The type Westinghouse kt relay is a polyphase compensated Type relief, which provides a single zone of phase protection and for three phase fault conditions. It provides instantaneous tripping for all combinations of phase two phase faults to phase two ground faults and three phase faults. Now the KT relay. In this case, the KV four relay is an old school relay. It's been around for some time and there's still a lot of them in existence today.

So I thought I would show you this just so you'd be familiar with the with the relay For more details, the relay manual will have to be consulted. These relays are slowly being replaced by the more modern Intel intelligent electrical devices the IED type relay, which we'll show you an example of in in the next few slides. This shows how the KT relay is connected. One Relay for each zone of protection zones. zone two and zone three. You'll notice that the current coils for zone three relay relay zone three relay, the current connections are reversed and this essentially provides the reverse looking quality that you want for your zone three really both zone two and zone three have auxiliary timing circuits, which you see here in the DC logic.

Okay, as promised, here is an example of in an intelligent electrical device or a solid state relay that is on the market today and in service. This one is a product of GE it's called the multiline d 60. There's other companies out there such as Siemens and sem Have equally if not better relays. But I thought I would just show this one as an example, to see the more modern type of relays that are available and these relays are basically small measuring devices with inboard computers that do a whole lot more than just do the impedance type measurements that the the old school relays provide. Anyway, this is the multiline multi lane d 60. It's line distance protection system, high speed transmission line protection with single phase and three pole tripping and reclosing capabilities.

Its applications are for overhead lines and underground cables even if there's different voltage levels, single and dual breaker circuits requiring single and or three pole Auto reclosing Independent synchro checks on reclosing. circuits with endzone power transformers are tapped transformer feeders can be included in this application. And it'll also provide a backup protection of sorts regenerators and transformers and reactors that are on the line as well. More specifically, these are the individual functions of the relay that you can see listed here. This relay is capable of the following functions if they are selected and they can be selected or not selected depending on the preferences of the utility that's maintaining this relay. It has a 21 G or a ground distance element it has 21 p for phase distance, synchronous synchronism.

For sinker, check relays on reclosing Faye's under voltage auxiliary under voltage reverse power, thermal overload, breaker failure protection, current disturbing and current disturbance detection, which is event recording recording triggered, ground instantaneous overcurrent protection neutral instantaneous overcurrent protection phase instantaneous overcurrent protection, negative sequence instantaneous overcurrent protection, ground time overcurrent neutral time overcurrent phase time overcurrent negative sequence time overcurrent circuit breaker AC circuit breaker monitoring compensated over voltage. This has to do with the variety of fact which I'm not going to go into detail here but basically it compensates for the current using to charge the line on medium, medium length feeder lines, it also has neutral over voltage protection phase over voltage protection, auxiliary over voltage protection, negative sequence over voltage and neutral directional overcurrent. So this really is really a system rather than described as just one really, it does a myriad of things, which is good because you can dial them in or dial them out as needed.

Besides providing all those protection functions, because there really is a highly accurate measuring device. It also has a built in fault locator. The integrated fault locator provides distance to the fault in kilometers or in miles. Parallel lines zero sequence current compensation and current compensation enable the D 60 to provide improved accuracy for fault distance measurements. It has single pole tripping as well as reclosing. It has communication aided schemes.

The D 60 supports different teller protection functions for fast fault clearance of any fault within the protected line. The following types of pilot aided schemes which pilot ated just means that they're communicating with each other over a distance. These are available in the D 60. Direct under reaching transfer trip. permissive under reach transfer trip provides to permissive overreach transfer trip functions hybrid, permissive overreach transfer tripping, directional comparison blocking scheme, directional comparison unblocking scheme and custom customizable version of the permissive or over permissive overreach transfer trip and DCB schemes. So, it provides many, many functions in the way of communications.

Again, they are selectable, you can choose to dial them in or dial them out. The D 60 also provides multi shot Auto reclosing up to four shots for single or three pole three pole Auto reclosing on all types of faults with in dependently programmable Dead End Time for each shot. Now most companies in at least in North America, usually use three, three pole tripping and reclosing. A low single pole tripping is available with this relay and you can use additional features of this relay include monitoring and metering. The D 60 includes high accuracy, metering, and recording for all AC signals voltage current power metering. All of this is built into the relay current and voltage parameters are available in total RMS magnitude, or fundamental frequency, magnitude and angle.

Remember, this relay is more than just a relay. It has a built in computer basically which is capable of providing readings in any format that you want. It also has a fault and disturbance recording capability. It will do sequence of events. It's a calligraphy us record up to 64 digital and up to 40 analog channels with events up to 45 seconds in length. It's also a data logger for disturbance recordings 16 channels up to one sample cycle per channel and it has a sophisticated fault reporting system to provide a summary of fault reporting as required.

It also has health diagnostics built into it so we will check itself out at the beach Getting or at the startup it will continually check connections and logic sets in the system, and it will report any kind of problems that would crop up via a skater or communication connected system. The communication system, the D 60 provides for secure remote data and engineering access making it easy and flexible to use and integrate into new and existing infrastructures. Fiber Optic Ethernet provides high bandwidth communications allowing low latency controls and high high speed file transfers of really fault and event recording information. The D 60 supports most popular industrial standard protocols that are required out there and this is just a shot of how the relay is connected to the system. Before you'd in the old school relays you had to be careful of the connections and whether you had line to ground and face to neutral and all the rest of it, connections per per relay and per relay zone.

All of that has been eliminated in these newer type relays. Essentially what you do is connect up a three phase set of voltages from your VPS or cvts. And you connect up your current sources that are required. And then you use a computer to dial up the various functions and and the relay itself deals with all three phases and mixes them and matches them and provides the protection that you require through digital techniques. You can connect to this relay with a computer running the provided software which they call the inner VISTA you are setup software. And you can do that locally with a laptop computer through the front panel rs 232 port that is on the relay or you can actually access the computer or sorry you can access the relay remotely via a modem connected to the RS 45 or Ethernet port on the rear panel of this relay.

So I hope this did not sound like a sales pitch for this type of or this really it is provided by GE and there are equally if not better, relays that are out there that are provided by Siemens or provided by Sal I happen to select this one just as an example. And just as I selected the old school key D relay as an example, just to let you know what is out there and what the capabilities are. For further details, I encourage you to contact the manufacturers and the manufacturers data on their various products that are out there. However, this will give you a good overview of what impedance or distance type really is. And this ends chapter 10