Advantages of SELF POWERED Overcurrent & Earth Fault Relays

Transcription

1 AL Advantages of SELF POWERED Overcurrent & Earth Fault Relays

2 1. INTRODUCTION Figg 1. Transformation center. Self-powered protections arise against the undeniable fact that transformation centers do not have a maintenance routine to ensure that the center is operative. The reasons for this situation are diverse, including: Lack of access to the center. Not all facilities are roadside. Some are buried, or in areas of difficult access. Lack of knowledge. Transformationn centers, ass already indicated, many times (50% or so depending on the country) are purchased by individuals, that ignore the maintenance e routine of these centers. Lack of qualified personnel. Power companies have qualified personnel, but their labors of maintenance are focused in the primary distribution centers, leaving transformation centers as a subsidiary task, since there is not enough qualified staff. Given this reality, the need for electronic equipments maintenance pass from a desire to a necessity. without Fig 2. Breaker with fuse. Within maintenance routines, most of them, or greatest need for them, is derived from the need to verify and check the status of the battery supply. Since the trip of transformation centers are always definitive, and there is no reclose, neither engines for coils reconection, there is the possibility of segregation switchgear, by means of a breaker or circuit breaker, whichh instead of having tripping coils, have tripping strikers.. The strikers are electromagnets that are loaded at the closing of the switchgear, and is required low-energy trigger to releasee them. Different models and tensions, and in general the selection of it is a compromise between mechanical security and tripping energy, but in general are a reliable and high quality element. However, in many installations the use of a striker is not always possible, since it assumes the mechanical modification of the mechanisms for locking and tripping of the breakers, and can usually come standardd with tripping coils. Thus, it is possible the use of accessory equipments whichh act as accumulators of energy to generatee the tripping of the coil. They are accessories that can be loaded prior to installation or on it, if available auxiliary power supply.. Fig 3. Tripping striker 2 / 5

3 This equipment guaranteed to keep tripping energy (30 J) at least 72 hours, it means, a weekend, and also, if found fully dischargedd it has a loading time sufficiently short (less than ten seconds) to have trip in the shortest time possible. Fig 4. TCM coil energy acumulator. Of course, the amount of energy used in thee trip, is directly related to the type of coil used, and how much less energy will require more remaining in the TCM, and thereby increasee the energy storage time. 2. SELF-POWER The main power in a self-powered relay comes from the passing through primary current in transformatiot on center itself. The primary current for feeding the center, besides being measured, is used for obtaining energy to feed the protection relays. This forces inn the other hand, to self-powered protection relays have very low power consumption, so that is not reflected on the line, and thus, the functionality of the equipment may not be as extensive as desired. Fig5.. Self powered relay In this case there are two types of self-powering g: 2.1. Different CTs for measuring and powering: In this case, we have two different cores with different constituent materials. Separating the core allows the relay to be operative with really low primary current levels. Currently, protection relays are getting supply current values of 5 amp single phase primary. In contrast, these devices have the disadvantage that in centers with high primary current levels, the relay must m evacuate more current. Finally it is noteworthy that the CT are specific and must be tuned to protection. Fig 6. Doble core CT for measuring and powering Unique CTs for measuring and powering: In this type of equipment, power comes from standard type CT /1 or /5. In a general way, are considered to be started (it means, be operative), with a level of single phase 0..2xIn. That is, if for example we have a CT 100/1, the relay will be operative from 20 primary amps. In this type of relays the CTs are standard and its only consideration is that a they should have sufficient VA to ensure protection startup. In any case,, this level is not excessive, 2VA usually sufficient, since the protection suits its internal load to passing through current. In the case of using standard CT /1 or /5, it was reported that should provide enough VA to feed the self-powered d protection relay. This also contributes to design relays that provide low resistance to the CT, it means, they charge little to the CT in order to have a technically and economically viable selection. It should be recalled in this section that in self-powered relays is very important to have separate internal power transformer for each phase. In a lot of relays there are savings in this point, grouping several feedings onn the same transformer. This means ncreasing significantly the single-phase starting level, because if you wire the t rest of the circuit, it will cause current circulation that will increase the startup level. Fig 7. Standardd CTs /1 or / / 5

4 In addition to the current powering is normal to have other supplies, which are considered secondary, but they have their importance: Alternate power supply. As being a transformation center is normal to have low voltage. The great advantage of including auxiliary voltage on self-powered relays is that if you have very resistive faults, below 0.2xIn, it is likely that the voltage is not compromised, and thus ensure the trip. Also in telecontrolled centers, powering the protection with auxiliary supply guarantees to have control and management of alarms, even when the passing through current is zero (especially at night or weekends). This is, if auxiliary power supply is guaranteed, this option allows to get lower tripping times. Direct power supply. There are models that have direct power at 24 Vdc. At first sight it seems not to have sense to fit self-powered protections with DC power supplies, but we'll see it has. There are centers that remote management is given by sms systems, and for them there is a small remote that is supplied with these DC levels. Certainly there are protection relays that operate at 24 Vdc, but the difference between a normal and a self-powered relay is consumption. Self-powered relays, operating at 24Vdc consume 20 times less than a normal relay. Also if the battery completely run out of energy, a self-powered relay will keep on tripping and a normal relay will not. Battery power supply. The KitCom is an adapter that allows to feed SIA relays from the front communication port, allowing also to communicate with the relay locally via RS232. Fig 9. Kitcom. 12 Vdc battery supply. The power comes from two AA batteries of 1.5 voltios, located at the bottom of it. The adapter has a small Dc/Dc source that increase the voltage to 12 Vdc required to operate the equipment. It is also worth mentioning the possibility of doing a test to the self-powered relays before putting then ON, to check the proper functioning of the hardware of the relay. Therefore, it is possible to feed the relays with the KitCom battery to access the relay test menu. This, coupled with the possibility of activating the trip contact from the test menu, allows verification of the trip circuit prior to the energization of the transformation center. 4 / 5

5 3. TRIPPING TIME The tripping time is very dependent on the available energy, and how it is designedd the self-powered relay. The energy available to power the relay will alloww to charge the tripping capacitorss in more or less time and, obviously, the sooner the capacitors are charged, the lower trip times. So, working on starting current values (0.2xIn),, the trip canbe delayed a second, while these times are going to be falling fastly while increasing passing through current. Thus, at rated current, this time may be 200 milliseconds, and reaches down to 60 milliseconds with three times the rated current. Logically, if the energy level required is lower, especially because it uses less power striker, these times may be lower. Also consider if the current is three-phase, reducing overall timee in half. Therefore, in a self-powered equipment if a fault occurs during service, the trip times are exactly the same as conventional equipment. So when you set the time of trip is done from the t worst of conditions, itt means, with the relay switched off. The starting time of the electronic is the other part to consider at the time of tripping. A relay in its normal boot sequence can take a considerable time in management and adjustments checking, and therefore self-powered relays have different boot sequences. In general, with low currents, start time is blurred with the energy needs of the trip, and in the other side, with high currents, where tripping energyy is abundant, the tripping time is marked by the startt of the electronic. This leads to design self-powered relays withh differentiated processors accordingg to their starting gear. The consideredd "normal start up" and considered "fast start up", being the t second ones the ones that get the reduction of the tripping times, adding of the boot time of the electronics and the time of accumulation of energy to make a right trip. In the following table can be seen different tripping times of the self-powered equipment /5, with different values of single phase and three phase currents SIAC5 Tiripping time (ms) Time (ms) dual power Time (ms) 3Phase self power & FastModel Time (ms) 3Phase self power Time (ms) 1Phase self power & FastModel Time (ms) 1Phase self power 0, , , x In / 5

6 FANOX ELECTRONIC, S.L. Parque Tecnológico de Bizkaia, Edificio 604 ES Derio SPAIN