background image

monitoring for loss of field voltage or current. For
generators that are paralleled to a power system,
the preferred method is to monitor for loss of
field at the generator terminals. When a genera-
tor loses excitation power, it appears to the
system as an inductive load, and the machine
begins to absorb a large amount of VARs. Loss
of field may be detected by monitoring for VAR
flow or apparent impedance at the generator
terminals.

The power diagram (P-Q plane) of Fig. 18 shows
the Basler BE1-GPS100 and BE1-40Q character-
istic with a representative setting, a representa-
tive generator thermal capability curve, and an
example of the trajectory following a loss of
excitation. The first quadrant of the diagram
applies for lagging power factor operation
(generator supplies VARs). The trajectory starts
at point A and moves into the leading power
factor zone (4th quadrant) and can readily
exceed the thermal capability of the unit. A trip
delay of about 0.2-0.3 seconds is recommended
to prevent unwanted operation due to other
transient conditions. A second high speed trip
zone might be included for severe
underexcitation conditions.

FIGURE 18. FOR LOSS OF FIELD THE POWER
TRAJECTORY MOVES FROM POINT A INTO THE
FOURTH QUADRANT.

When impedance relaying is used to sense loss
of excitation, the trip zone typically is marked by
a mho circle centered about the X axis, offset
from the R axis by X'd/2. Two zones sometimes
are used: a high speed zone and a time delayed
zone.

FIG. 19. LOSS OF EXCITATION USING IMPEDANCE
RELAY.

With complete loss of excitation, the unit will
eventually operate as an induction generator with
a positive slip. Because the unit is running above
synchronous speed, excessive currents can flow
in the rotor, resulting in overheating of elements
not designed for such conditions. This heating
cannot be detected by thermal relay 49, which is
used to detect stator overloads.

Rotor thermal capability can also be exceeded for
a partial reduction in excitation due to an operator
error or regulator malfunction. If a unit is initially
generating reactive power and then draws reactive
power upon loss of excitation, the reactive swings
can significantly depress the voltage. In addition,
the voltage will oscillate and adversely impact
sensitive loads. If the unit is large compared to
the external reactive sources, system instability
can result.

Thermal Protection

Fig. 20 shows the Basler MPS200, BE3-49R, or
BE1-49 relay connected to a resistance-tempera-
ture detector, embedded in a stator slot. Relay
models are available for either  copper or platinum
RTDs. The relay provides a constant-current
source to produce a voltage across the RTD and
includes the means to measure that voltage
(proportional to temperature) using separate leads.
The relays have trip and alarm set points, and the
MPS200 can provide readout of present tempera-
ture.

11

Содержание BE1-1051

Страница 1: ...GeneratorProtection ApplicationGuide...

Страница 2: ...ign of protective relaying systems He worked for Consolidated Edison Company for ten years as a System Engineer He has served as a private consultant since 1982 Updates and additions performed by vari...

Страница 3: ...it is rather expected that a 500kW 480V standby reciprocating engine will have less protection than a 400MW base load steam turbine unit One possible common dividing point is that the extra CTs neede...

Страница 4: ...ral VFG in Fig 1 Assuming an impedancegroundedgeneratorwhere Z0 SOURCE and ZN ZWINDING the current level is directly proportional to the distance of the point from the generator neutral Fig 1 a so a f...

Страница 5: ...rcuit or setting the relay fairly insensitively FIGURE 2 GROUND FAULT RELAYING GENERATOR LOW IMPEDANCE GROUNDING The neutral CT should be selected to produce a secondary current of at least 5A for a s...

Страница 6: ...gh rejection of fundamental frequency voltage FIGURE 6 GROUND FAULT NEAR GENERATOR NEUTRAL REDUCES THIRD HARMONIC VOLTAGE IN GENERATOR NEUTRAL DROPPING OUT 27 3N The 27 3N performs a valuable monitori...

Страница 7: ...ult as seen by the generator neutral shift sensing relay 59N leading to a generator trip Alternatively assume that the VT corner e g phase A has been grounded If phase B or C fault to ground the fault...

Страница 8: ...2 100 5 from the neutral When feeder cables are connected to the gen erator bus the additional capacitance dictates a much lower level of grounding resistance than achieved with a unit connected case...

Страница 9: ...hout pre loading For example assuming a pre fault 1pu rated load at 30 degree lag at one second the 3 phase fault value would be 2 4 times rated rather than 1 75 timesrated 1 30 1 75 90 2 4 69 Under t...

Страница 10: ...edapproach inhibits operation until the voltage drops below a preset voltage It should be set to function below about 80 of rated voltage with a current pickup of about 50 of generator rated Since the...

Страница 11: ...imes tap CDS220 or 0 4A 87G is representa tive of a recommended setting for a moderate mismatch in CT quality and burden Fig 13 also shows 51V relays to back up the 87G and external relays and breaker...

Страница 12: ...nchroniz ing when the generator is initially slower than the system Since motoring can occur during a large reactive power flow the real power component needs to be measured at low power factors The B...

Страница 13: ...y a mho circle centered about the X axis offset from the R axis by X d 2 Two zones sometimes are used a high speed zone and a time delayed zone FIG 19 LOSS OF EXCITATION USING IMPEDANCE RELAY With com...

Страница 14: ...r during a fault To prevent a 60FL from being declared during loss of station power it may be necessary to allow a 3 phase 60F to be declared only when some low level of load current exists FIGURE 22...

Страница 15: ...ach set point may be set to recognize either over frequency or underfrequency Multiple frequency set points are available in the BE1 81O U BE1 GPS100 BE1 951 and BE1 1051 Another common need for frequ...

Страница 16: ...ld be employed where protection independent of the plant is desired In this case the 67 relays would be placed in the switchyard rather than in the control room While directional overcurrent relay 67...

Страница 17: ...reaker depending on the type of fault that is detected For instance if the generator is protected by a 51V and an 87G and only the 51V trips it may be assumed that the fault is external to the generat...

Страница 18: ...EXAMPLE OF BARE MINIMUM PROTECTION LOW IMPEDANCE GROUNDING Fig 30 shows the suggested minimum protection with low resistance grounding It includes differential protection which provides fast selectiv...

Страница 19: ...ssive generator reactive absorption Ther mal relay 49 protects against stator overheating due to protracted heavy reactive power demands and loss of generator cooling Even if the excitation system is...

Страница 20: ...voltage balancerelay 60 field ground relay 64F frequency relay 81 and the 27 50 62 relay combination for inadvertent energization protection Relay 51GN provides a second means of detecting stator gro...

Страница 21: ...ures 34 through 37 show the BE1 GPS100 and BE1 CDS220 applied to generator protection Due to logic complexity full details are not shown Details of these applica tions may be found in the respective i...

Страница 22: ...20 FIGURE 35 BE1 GPS100 APPLIED TO HIGH IMPEDANCE GROUNDED GENERATOR HI_Z_GND PREPROGRAMMED LOGIC SEE INSTRUCTION MANUAL FOR LOGIC DETAILS...

Страница 23: ...FIGURE 36 BE1 CDS220 APPLIED TO GENERATOR FOR 87 PHASE 87 NEUTRAL AND 51 PHASE NEUTRAL GROUND AND NEGATIVE SEQUENCE 21...

Страница 24: ...s typical settings for use as a starting point in the setting determi nation procedure The proper settings are heavily influenced by the specifics of each application Typical settings are also used as...

Страница 25: ...urrent 49 20 StatorTemperature RTD Lower 95 C upper 105 C 50 87 12 Differentialviaflux PU 10 INOM or less if 1A relay may be used summationCTs 50 27 IE 24 InadvertentEnergization 50 0 5A 10 INOM Overc...

Страница 26: ...75 100 INOM GEN Definite Time 0 1 0 25 sec InadvertentEnergization Inst 200 INOM GEN 81 21 Over underfrequency Generator protection 57 62Hz 0 5s Island detection 59 61Hz 0 1s 87G 13 GeneratorPhase BE1...

Страница 27: ...9 59 X X X X X X 59N 27 3N 59N 59P 4 4 4 60FL 60 X X X 67IE 67 X X 81 81O U 81O U X X X X X 87G 87G X 87N 67N 87UD 87T X 1 50 51G Indicates a relay that monitors a ground CT source 2 50 51N Indicates...

Страница 28: ...54 2341 Fax 1 618 654 2351 BaslerElectricInternational P A E Les Pins 67319 Wasselonne Cedex FRANCE Phone 33 3 88 87 1010 Fax 33 3 88 87 0808 If you have any questions or need additionalinformation pl...

Отзывы: