Synchronized metrology in power generation and distribution networks
Phasor Measurement Units (PMUs) tend to be specialized and expensive—relegated to only key points in power distribution networks, and are generally reliant on GPS technology. The present disclosure details how any smart meter—using wireless communication—can perform sub-microsecond-grade synchrophasor measurements. Other aspects concern smart meter-based determination of A, B or C phase of the tri-phase power network. This can involve count-stamp enabling message packets sent to and/or from a smart meter, and then associating such count-stamps to local measurements of power phase by a metrology unit. Once a network of such enabled smart meters and other devices is formed, sub-microsecond metropolitan-wide and entire region-wide synchronizing time standard can calibrate local measurements of power phase, where simple A, B and C phase determination is one low hanging fruit application of such. Low cost aggregate monitoring of metropolitan-wide synchrophasors promises a next chapter of importance for that relatively recent art.
1. A method useful in determining an electric power phase relationship between two devices, a first device comprising a power meter device connected to a power distribution system and a second device comprising another device connected to the power distribution system, the method characterized by processing one or more messages received from the second device, together with zero crossing data generated by the first device, to determine relative timing between zero crossings of power signals sensed at said devices, wherein the message received from the second device is clock-stamped by the first device.
2. The method of claim 1 that further includes, from said relative timing, determining whether the power signal at the first device is (a) in phase with the power signal at the second device; (b) leads the power signal at the second device by 120 degrees; or (c) lags the power signal at the second device by 120 degrees.
3. The method of claim 1 in which both of said devices comprise power meter devices.
4. The method of claim 1 that includes count-stamping the message(s) received from the second device, by reference to clock counts from a free-running clock in the first device that runs at 100 KHz or more.
5. The method of claim 1 that includes determining relative timing between the zero crossing measurements to an accuracy of better than 25 microseconds.
6. The method of claim 1 wherein at least one of said devices is devoid of a GPS receiver.
7. The method of claim 1 wherein the message received from the second device is clock-stamped.
8. The method of claim 7 in which the message received from the second device is clock-stamped by the second device.
9. The method of claim 7 in which the message received from the second device is clock-stamped by the second device to indicate a zero-crossing event at the second device.
10. A method of determining phase relationship among power meters, the method comprising the acts:
collecting count stamped messages transmitted between nodes in a network including at least first and second power meters, the messages including zero crossing measurements of a power signal sensed at a corresponding power meter;
from the count stamped messages, determining relative timing among clocks within the power meters; and
from the relative timing and zero crossing measurements, determining relative phases between the power meters;
wherein the power meters include a first clock for zero crossing measurements and a second clock for count-stamping a message communicated with another node in the network, and the method further includes determining relative timing between said first and second clocks.
11. The method of claim 10 wherein the zero crossing measurements within the first power meter and the count-stamping of a message by the first power meter are made relative to a common clock within the first power meter.
12. A power meter comprising:
a metrology unit for measuring zero crossing of a power signal; and
a communication unit, in communication with the metrology unit for collecting zero crossing measurements and communicating count stamped messages including the collected zero crossing measurements to a remote node for determining relative phase between the power meter and another power meter;
wherein the communication unit is in communication with a local clock for count-stamping messages upon transmission.
13. A power meter comprising:
a metrology unit for measuring zero crossing of a power signal; and
a communication unit, in communication with the metrology unit for collecting zero crossing measurements and communicating count stamped messages including the collected zero crossing measurements to a remote node for determining relative phase between the power meter and another power meter;
wherein the communication unit is in communication with a local clock for count-stamping messages upon receipt.
14. A power meter comprising:
a metrology unit for measuring zero crossing of a power signal; and
a communication unit, in communication with the metrology unit for collecting zero crossing measurements and communicating count stamped messages including the collected zero crossing measurements to a remote node for determining relative phase between the power meter and another power meter;
wherein the communication unit is in communication with a second power meter for receiving count-stamped messages and for determining phase relative to the second power meter.
15. A power meter comprising:
a metrology unit for measuring zero crossing of a power signal;
a communication unit, in communication with the metrology unit for collecting zero crossing measurements and communicating count stamped messages including the collected zero crossing measurements to a remote node for determining relative phase between the power meter and another power meter; and
a first clock for providing time for the zero crossing and a second clock for count-stamping the messages.