Monitoring of Angular Separation in Power system: Part 6
Next method through which system operators can have angular separation information is through Phase angle transducer.
Phase angle transducers measure the phase relationship between a current and a voltage or two voltages. The transducer converts the phase angle value to either a DC mA or DC voltage output which is directly proportional to the input signal. ?This information can be converted to digital values by means analog to digital transducer and sent to control center for monitoring purposes. Here one major factor is that the input signals should be local in nature.
So, if there are two voltage inputs provided to phase angle transducer within a substation then it will provide angular separation between these two voltage inputs. And transferring this phase angle difference to control center will help system operators in real-time angular separation information to the system operator.
The angle transducer will take one signal as a reference to calculate the phase angle separation with the second input.?The principle of calculation will remain the same as the Synchrocheck relay however here the angular difference will be transferred to the control center for monitoring. ?
The beauty of this limitation of local input can be harnessed by system operators for monitoring some key important phase angle separation in power systems. Let us have a look at where it can be utilized.
Example: Phase angle transducer usage at HVDC Back-to-Back substation: HVDC back-to-back substation basically connects two power system (grids) asynchronously. However, with grid expansion and they may have AC interconnections and get in synchronism. ?Such HVDC B-t-B station still plays a key role due to their controllability of power transfer and two different grid nodes are available near to each other. The phase angle difference between two sides of grid at this HVDC B-t-B substation can be easily monitored using phase angle transducer. Any change in this angle will directly provide a measurement of the ongoing changes in both grid impacting AC tie lines flow interconnecting them. High angle separation will indicate large power flow and characteristic of AC tie line transfer based on which HVDC B-2-B can be used for modulating its power to reduce the angle.
One of the best examples of such usage by power system operators is discussed in detail in the vintage paper available in the link:
S. K. SOONEE*, S.R NARASIMHAN, R.K. PORWAL, S.KUMAR, R. KUMAR, V. PANDEY, "Application of phase angle measurement for real time security monitoring of Indian Electric Power System- An Experience", CIGRE Paris Session 2008.
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This phase angle transducer can also be used at other key monitoring which includes :
1.???Between bus and line voltage :?Locations for synchronization of subsystems within synchronous system or important tie line within synchronous system
2.???Between two buses at the same AC substation and operating in split mode.
3.???Substation having two voltage levels that are not physically connected.
4.???Detection of Out of step condition of generating unit
This method is effective for monitoring of standing phase angle information in a synchronous power system as it will vary only with changes in load/gen balance, power flow on tie lines etc.
For asynchronous systems, ?angular separation at HVDC B-t-B node will rotate with frequency slip speed and sending such time varying signal to control center in the last decade was one challenge with available communication system. However, during black start support by bypassing HVDC B-t-B such angle from transducer can be of significant help. The issue of communication system bandwidth and latency now has been overcome with OPGW based communication system in the present scenario for power system.
With advent of technology and OPGW based communication system now real-time phase angle measurement technology has also advanced and Wide area measurement system (WAMS) has come. WAMS system help system operators in real-time monitoring phase angle separation between any two nodes in the power system. This will be discussed in part 8 of this series. This phase angle transducer still has very important role and used in many industrial power system.