Universidad Michoacana de San Nicolás de Hidalgo
4. CÁDIZ Y EL CONSTITUCIONALISMO IBEROAMERICANO
2.8.1 Functional Description
General The overcurrent time protection represents the short-circuit protection for small or low-voltage machines. For larger machines it is used as back-up protection for the machine short-circuit protection (differential protection and/or impedance protection).
It provides back-up protection for network faults which are not promptly disconnected and thus may endanger the machine.
The 7UM62 relay allows to choose between the input transformers of side 1 and side 2 for allocation of the inverse-time overcurrent protection function. This choice is made during configuration (see Section 2.2).
In generators where the excitation voltage is derived from the machine terminals, the short-circuit current subsides quickly in the event of close-up faults (i.e. in the generator or unit transformer range) due to the absence of excitation voltage the current decreases within a few seconds to a value below the pick-up value of the overcurrent time protection. In order to avoid a drop out of the pickup, the positive-sequence component is monitored additionally. This component can influence the overcurrent detection according to two different methods. The influence of the undervoltage can be switched off.
The protective function operates, depending on the ordering variant, with an inverse current-tripping characteristic according to the IEC or ANSI standards. The
characteristic curves and the corresponding formulas are represented in Technical Data (Figures 4-1 to 4-3 in Section 4.3). If one of the inverse characteristics (IEC or ANSI) are configured, the definite-time stages I>> and I> can be additionally effective (see Section 2.6 and 2.7).
Pickup / Trip
Each phase current is compared individually with the commonIpsetting value. If a current exceeds 1.1 times the set value, the stage picks up and is signalled on a per phase basis. The r.m.s. values of the fundamental component are used for the pickup.
During the pickup of an Ip stage, the tripping time is calculated from the flowing fault current by means of an integrated measuring procedure, depending on the selected tripping characteristic. A trip command is transmitted after this time expires.
Dropout The dropout of a picked up stage is performed as soon as the value falls below approximately 95 % of the pickup value (i.e. 0.95⋅1.1 = 1.045⋅ setting value). The timer will start again for all new pickups.
Undervoltage Consideration
The inverse O/C time protection is equipped with a undervoltage detection that can be disabled. This function can influence the overcurrent detection in two different ways:
• Voltage controlled:
If the value falls below a settable voltage threshold, an overcurrent stage with a lower pick-up value is enabled.
• Voltage restraint:
The pickup threshold of the overcurrent stage depends on the voltage level. A lower voltage reduces the current pick-up value (see Figure 2-16). A linear, directly proportional dependency is realized in the zone between U/UNom= 1.00 and 0.25.
Consequently, the following rule applies:
Inverse-Time Overcurrent Protection (ANSI 51V)
:
Figure 2-16 Pick-up Value Voltage Restraint
TheIp reference value is decreased proportional to the voltage decrease.
Consequently, for a constant currentItheI/Ip ratio is increased and the trip time is reduced. Compared with the standard characteristics represented in Section 4.3, the tripping characteristic shifts to the left side in relation to the decreasing voltage.
The changeover to the lower pick-up value or the reduction of the pickup threshold are performed on a per phase basis. The assignments of voltages to the current-carrying phases are represented in Table 2-5. As the protection used in the generator range is incorporated in the network grading plan, the phase shift of the voltages by the unit transformer must also be considered. This facts requires principle distinction between a unit connection and a busbar connection, which must be communicated to the device by means of the parameter0213 SCHEME. As phase-to-phase voltages are referred to in any case, faulty measurements in case of earth faults are avoided.
In order to avoid an unwanted operation for a voltage transformer fault, a blocking function miniature circuit breaker as well as via the device-internal measuring voltages failure detection (”Fuse–Failure–Monitor”, also refer to section 2.38.1.4).
Figure 2-17 illustrates the logic diagram of the inverse O/C time protection without undervoltage influencing, whereas the Figures 2-18 and 2-19 illustrate the logic diagrams with undervoltage influencing.
I U( )pickup Ip U Uno m
---⋅
= for 0.25 U
Unom --- 1.00
≤ ≤
I U( )p ic ku p = Ip⋅1.00 for 1.00 U Unom --- ∞
≤ ≤
I U( )pickup = Ip⋅0.25 for 0.00 U Unom --- 0.25
≤ ≤
U U⁄ nom Factor
1.0
0.25 0.5 0.75
0.25 0.5 0.75 1.0
where Unom – Generator nominal voltage = parameter0251 UN GEN/MOTOR I(U)pickup – Voltage-influenced pickup value
Ip – Pick-up value of inverse characteristic parameter = parameter1402 Ip
Table 2-5 Control Voltages in Relation to the Fault Currents
Current Voltage
Busbar connection Unit connection IL1 UL1– UL2 ((UL1– UL2) – (UL3– UL1)) /√3 IL2 UL2– UL3 ((UL2– UL3) – (UL1– UL2)) /√3 IL3 UL3– UL1 ((UL3– UL1) – (UL2– UL3)) /√3
Figure 2-17 Logic Diagram of the Voltage-Controlled Inverse O/C Time Protection without Undervoltage Influencing
Tripping matrix
>BLOCK O/C Ip FNo. 01883
&
1403 T Ip 1403 T Ip 1403 T Ip
&
Pickup IL1
(Pickup)
(Pickup)
&
FNo. 01900 O/C Ip TRIP
FNo. 01892 O/C Ip BLOCKED
FNo. 01897 O/C Ip Fault L2
FNo. 01896 O/C Ip Fault L1
FNo. 01898 O/C Ip Fault L3
OR
FNo. 01899 O/C Ip pick.up
OR
TMin TRIP CMD
Inverse-Time Overcurrent Protection (ANSI 51V)
Figure 2-18 Logic Diagram of the Voltage-Controlled Inverse O/C Time Protection
The changeover to the lower current pick-up value in case of decreasing voltage (loop release) is performed on a phase by phase basis according to table 2-5.
1403 T Ip 1403 T Ip
1402 Ip
Tripping matrix
>BLOCK O/C Ip FNo. 01883
&
1403 T Ip
&
&
FNo. 01900 O/C Ip TRIP
FNo. 01892 O/C Ip BLOCKED
FNo. 01897 O/C Ip Fault L2 FNo. 01896 O/C Ip Fault L1
FNo. 01898 O/C Ip Fault L3 1402 Ip
>FAIL:Feeder VT FNr. 000361 Fuse Failure
Loop release IL1
IL2
IL3
UL1 UL2 UL3
1402 Ip
FNo. 01899 O/C Ip pick.up
OR
OR
OR
TMin TRIP CMD
Figure 2-19 Logic Diagram of the Voltage-Restraint Inverse O/C Time Protection
The reduction of the current pick-up threshold in case of a decreasing voltage (control voltage assignment) is performed phase by phase according to Table 2-5.
2.8.2 Setting Hints
General The inverse O/C time protection is only effective and accessible if this function was allocated to the input CTs of either side 1 or side 2 during configuration (see Section 2.2), i.e. if address0114 O/C PROT. Ip=with IEC-characteristic on side 1,with ANSI-characteristic on side 1,with IEC-characteristic on side 2orwith ANSI-characteristic on side 2was set.Disabledis selected if the function is not needed.
Ip overcurrent stage
Address1401 O/C Ipis used to switch the functionONorOFF, or to block only the trip command (Block Relay). It must be noted that, for the inverse O/C time protection, a safety factor of about 1.1 has been included between the pick-up value and the setting value. This means that a pickup will only occur if a current of about 1.1
1403 T Ip
FNo. 01883 FNo. 01892
O/C Ip BLOCKED
Inverse-Time Overcurrent Protection (ANSI 51V)
times of the setting value is present. The function will reset as soon as the value falls below 95 % of the pick-up value.
The current is set at address1402 Ip. The maximum operating current is of primary importance for the setting. A pickup caused by an overload must be excluded, as the device operates in this mode as short-circuit protection with correspondingly short relay times and not as overload protection.
The corresponding time multiplier for configuration of IEC characteristics (address 0114 O/C PROT. Ip=IEC Side n) is accessible at address1403 T Ip. At address1405 IEC CURVE, 3 IEC characteristics can be set.
The time multiplier for configuring ANSI characteristics (address0114 O/C PROT.
Ip=ANSI Side n) can be found at address1404 TIME DIAL: TD; parameter1406 ANSI CURVE offers a choice between 5 ANSI characteristics.
The time multipliers must be coordinated with the network grading plan.
The time multipliers can also be set to∞. If set to infinity, the stage will not trip after pickup. However, the pickup is signalled. If the Ip stage is not required at all, set at the address0114 O/C PROT. Ip=Disabled, or switch the function out by setting1401 O/C Ip =OFFduring configuration (see Section 2.2).
The address1408serves to predefine theU<pick-up value for the undervoltage trip of the Ip pickup value for voltage-controlled inverse O/C time protection/AMZ (parameter1407 VOLT. INFLUENCE=Voltage controlled). The parameter is set to a value situated just below the lowest phase-to-phase voltage permissible during operation, e.g. from 75 to 80 V. In this context, the same rules apply as for the undervoltage seal-in of the definite O/C time protection (see also subsection 2.6.2).
If at address1407 VOLT. INFLUENCE=WithoutorVoltage restraintis set, the parameter1408has no function.
2.8.2.1 Settings of the Inverse O/C Time Protection
The following list indicates the setting ranges and the default settings of a IN= 1 A secondary nominal current. For a secondary nominal current of IN= 5 A, these values must be multiplied by 5. Consider the current transformer ratios when setting the device with primary values.
Addr. Setting Title Setting Options Default Setting Comments
1401 O/C Ip OFF
ON
Block relay for trip com-mands
OFF Inverse O/C Time Protection Ip
1402 Ip 0.10..4.00 A 1.00 A Ip Pickup
1403 T Ip 0.05..3.20 sec;∞ 0.50 sec T Ip Time Dial
1404 TIME DIAL: TD 0.50..15.00;∞ 5.00 TIME DIAL: TD
1405 IEC CURVE Normal Inverse
Very Inverse Extremely Inverse
Normal Inverse IEC Curve
2.8.2.2 Information for the Inverse-Time Overcurrent Protection
1406 ANSI CURVE Very Inverse
Inverse
Moderately Inverse Extremely Inverse Definite Inverse
Very Inverse ANSI Curve
1407 VOLT. INFLUENCE without
Voltage controlled Voltage restraint
without Voltage Influence
1408 U< 10.0..125.0 V 75.0 V U< Threshold for Release Ip
Addr. Setting Title Setting Options Default Setting Comments
F.No. Alarm Comments
01883 >BLOCK O/C Ip >BLOCK inverse O/C time protection
01891 O/C Ip OFF O/C protection Ip is switched OFF
01892 O/C Ip BLOCKED O/C protection Ip is BLOCKED
01893 O/C Ip ACTIVE O/C protection Ip is ACTIVE
01896 O/C Ip Fault L1 O/C fault detection Ip phase L1 01897 O/C Ip Fault L2 O/C fault detection Ip phase L2 01898 O/C Ip Fault L3 O/C fault detection Ip phase L3
01899 O/C Ip pick.up O/C Ip picked up
01900 O/C Ip TRIP O/C Ip TRIP
Thermal Overload Protection (ANSI 49)