using superimposed principles (delta) in protection...
TRANSCRIPT
USING SUPERIMPOSED PRINCIPLES (DELTA) IN PROTECTION TECHNIQUES IN
AN INCREASINGLY CHALLENGING POWER
NETWORK
Patricia Horton, Simon Swain– GE Grid Solutions
2017 Texas A&M Protective Relay Conference
Introduction• Superimposed techniques a lso called Delta or Incremental techniques
have been used for more than 30 years in protective relays
• Directional Comparison relays were popular in the 80s and 90s. They were called “Directional Wave relays” Some of those relays use to quote fault detection time as little as 2-5 ms
Superimposed ( DELTA ) technique
Subtracting a value of the signal, before a change from its corresponding value after the change will produce a signal that represents the change.
A Change signal produced in this way is a superimposed component.
Superimposed voltage and current
When a fault occurs on a power system, changes occur in the current and voltage signals which produce superimposed components
Sequence networks for a ph-gnd fault
Z SA1 ZL1 ZSB1
∆V1
∆I1∆I1
ZSA2 ZL2 ZSB2
∆V2
∆I2∆I2
ZSA0 ZL0ZSB0
∆V0
∆I0∆I0
IF / 3
E
Source Voltages appear short-circuited as they do not change during the fault
Voltage generator represents voltage change at fault location and is the Vph-n at fault point prior to the fault occurrence
DELTA for External faults (1)
The fault inception is represented by the closing of the switch S which connects the Superimposed voltage source ∆E, whose magnitude is the change in voltage at the fault point.
This causes a Superimposed current ∆I to flow in the Superimposed circuit
Equivalent circuit in which all signals are Superimposed Components
DELTA for External faults (2)Positive directions as defined per relay location ∆Ir
Zsa ZlEnd BEnd A
∆Ir
Zsb
∆Vr ∆Vr
∆I
Zsa * ∆Ir + ∆Vr = 0 ( Zsa + Zl )* - ∆ Ir + ∆Vr = 0
ZsaVIEndA r
r∆−
=∆:ZlZsa
VIEndB rr +
∆=∆:
+
- -
+
E
S∆I
DELTA for Directional Determination (1)
∆V
- ∆V
∆I
∠ Zs60°
RCA
For a Forward ∆I lags –∆V according to the characteristic angle of the source impedance behind the relay angle.
ZsaVIEndA r
r∆−
=∆:
DELTA for Directional Determination (2)This is ABN solid fault behind the relay location in a parallel line with heavy load flowing out from the Relay location.
Fault and prefault vectors shows how a -30° conventional memory directional line sees the fault in the forward direction
Delta directional sees the fault in the reverse direction
Using Deltas for phase selection (1)A way to use Delta principles to do phase selection is comparing the magnitudes of the three phase-to-phase superimposed currents against a threshold
This is a an example for phase A to ground fault
A single phase-to-ground fault produces the same superimposed current on two of these signals and
zero on the third
Using Deltas for phase selection (2)
This is a an example for phase AB fault
A phase-to-phase or double phase-to-ground fault produces one signal which is larger than the other two
Threshold is dynamic. For instance they are automatically increased if all current phases are less than rated current to a % of the highest phase current to prevent sporadic operation during high levels of sub-synchronous frequencies
DELTA for power swing detection (1)
PH1
PH2
Fault
PH1 : Phase 1, starts PH2 and primes PSB. Compares current value with previous 2 cycles
PH2 : Phase 2, enables distance elements. Compares current value with pre-fault value.
DELTA for power swing detection (2)Powerswing
Fault
PH1
PH2
PSB act ive& minimumthresholdincreased
PSB removedIncluding 3 ph faults
3cycles
Delta Directional Comparison protection
This has been a protect ion which has become less popular over the years as Distance protect ion have similar operat ing t imes
Delta Direct ional protect ion
Delta base Distance protection
DELTA for Z source determination
Zsa ZlEnd BEnd A
∆Ir
Zsb
∆Vr∆I
Zsa * ∆Ir + ∆Vr = 0
-
+
E
S
r
r
IVZsa
∆∆−
= With the calculation of the source impedance behind the IED, estimation of the short
circuit level is possible given a suitable event in the grid.
DELTA for SSC HVDC AC/DC Con. StationIf a HVDC converter is connected to a weak AC grid relative to the DC power, problems with power frequency stability and voltage can occur
The weaker the AC grid is, the greater the AC/DC interact ions
Short Circuit Ratio (SCR) = ratio of the AC SC to the size of DC converter power.
If SCL of the grid is 1000MVA and the size of the converter is 200MW :SCR is 1000/200 = 5.
SCR levels are categorized : high, Low and very low
A large European utility, SC Capacity Concept
• Calculate RoCof V&I due to “downstream” event (not changing source V & Z)
• Filter switching events are downstream. SCADA switching event sent to PhasorPoint to initiate SCC calculation.
ZIV
=∆∆
−
Benefit s• Ensure SCC large enough at connection
to HVDC• Relax generation dispatch constraints• Address uncertainties in model based
SCC with high renewable generation • Ensure SCC below C/B ratings• Filter switching can be initiated manually
when SCC value needed• Historical SCC for planning
Delta SCC prediction in active DN• DN with DG and loads with bi-directional power flow and plug-and-play functionality
can increase fault levels which possibly exceed the opening capacity of the related CBs
• On the other hand, when the distribution feeders loose the connexion with the grid, the fault level could be extra lower than the normal fault level.
With the changing rate of the load or an event, is possible to predict Current Fault Level and location and take respective action
• Superimposed components (delta) based principle has been used in commercially available relays for more than three decades successfully protecting the transmission lines .
• Delta directional technique have been complimented by delta based phase selection and delta current based power swing technique, to provide fast and secure operations for most faults in the power system even when they are complex.
• Most recently this principle is being used to assist smart grid in functions such as fault level prediction
Conclusions
Thank You
Questions?