EPOCHS
The Electric Power and Communication Synchronizing Simulator
Ken Hopkinson, Renan Giovanini, Xiaoru Wang, Ken Birman, Jim Thorp,
and Denis Coury
EPOCHS Sumary
EPOCHS is a middleware platform that integrates communication and
electric power simulators allowing users to test scenarios in a
combined environment. The system is agent-based allowing users to
create complex scenarios. EPOCHS fulfills a real need in the
electric power industry. Up until now, there has not been any way
to accurately test electric power communication systems. There is
an increasing interest in the use of communication technology to
enhance electric power systems making this an important niche.
How EPOCHS Works
EPOCHS uses a run-time infrastructure (RTI) as a middle layer between
each simulator. EPOCHS currently supports NS2 as its
communication subsystem and both PSCAD/EMTDC and PSLF as its power
subsystems. User-written modules are placed in the agent
subsystem and interact with other simulations through messages through
the RTI. This leads to an architecture that looks like the one
shown here. EPOCHS uses a time-stepped approach meaning that all
simulators run for a fixed amount of simulation time and then
halt. Simulators exchange information until they receive
notification from the RTI allowing them to proceed to the next time
step. Both PSCAD/EMTDC and PSLF simulate their targets by solving
differential equations in a stepped manner making this a natural
approach.
A Sample EPOCHS Application
We have created a small backup relay test system to illustrate how
EPOCHS can be used to investigate power system scenarios. Relays
and breakers together can be thought of as the fuses in your
house. They are supposed to trip to isolate problems when power
anomalies occur. The relay detects abnormal situations and then
instructs breakers to act. Breakers are the devices that actually
trip lines. The goal is to trip breakers so that the smallest
possible problem area is taken out of service until the situation
corrects itself or a repair crew can be disbatched. Power system
equipment is traditionally made up of autonomous units that sense the
environment and make decisions based solely on local readings. We
added communication to backup relays so that each exchanged local
information with their neighbors at regular intervals. In this
type of environment, we can take a large system like the New York Power
Pool, zoom in to a small area like the one used as our example power
system, and still receive a representative sample of how our scheme
behaves making it an ideal first trial for the EPOCHS
environment. We would like to emphasise that EPOCHS is capable of
simulating much larger scenarios if the situation calls for it.
In this case, we have created five buses. The first and last
bus are both connected to a generator. There are four
transmission lines between the first and last bus. Distances
listed in kilometers are here to give a sense of how long transmissions
lines are in realistic scenarios, but they do not have a large effect
on the environment in question as power travels at close to the speed
of light. Each bus has one or more relays connected to it labeled
R1 to R8. There are also a series of breakers labeled B1 to
B8. In our scenario, a fault has occured between the bus labeled
M and the bus labeled N. That fault is marked with an X and is
labeled with an F. This fault might be a lightning bolt causing
line disruptions. We are assuming that either a relay or breaker
has failed to act appropriately and that it is the job of the backup
relay to take action to clear the fault.
Our backup agents are each equipped with a series of simple rules
that they follow. The rules are designed to detect problems and
determine whether or not the primary relay has responded
appropriately. If it has not and enough time has passed then the
backup relay will take action.
Relays send a message containing their current state with their
neighbors once per time step using a UDP packet.
In this example, the fault in line MN occurs at time 0.3
seconds. The backup relay 5 agent immediately detects the
abnormal situation and then waits to see if the primary relay/breaker
combination will take action. After the breaker clearing time has
passed, the breaker takes action clearing the fault. Backup relay
5 trips and then sends an immediate trip command to relay 4.
Relay 4's breaker fails to trip and the failure cascades to backup
relay 3 which also trips. This whole sequence of events takes
much less time than would be necessary using a traditional scheme
without communication.
All agent actions took place in user-written modules in the Agent
section of the EPOCHS systems. The agents perceive a unified
environment that is presented to them through read and write requests
made on their behalf by the AgentHQ. Communication takes place
inside NS2 with each relay/breaker location represented as a
communication node. Transmission lines are treated as ethernet
lines. PSCAD/EMTDC serves as the power simulator and all power
state is read/written through the EPOCHS RTI.
A more detailed description of this scenario can be found under the
EPOCHS Publications section below.
EPOCHS Availability
We are in the process of modifying the EPOCHS source code to make it
easy for others to modify and use for their own power and communication
scenarios. We hope to complete this process in the near future
and will make the system available to the public at that time.
EPOCHS Publications
The sample application outlined above appeared at a conference in the
Fall 2002. A publication on the EPOCHS infrastructure itself is
currently in preparation.
Wang, X.R.; Hopkinson, K.M.; Thorp,
J.S.; Giovanini, R.; Birman, K.; Coury, D., Developing an
Agent-based Backup Protection System for
Transmission Networks. First International Conference on Power
Systems and Communication Systems Infrastructures for the Future. 23-27
of September 2002, Beijing, China.
Page Last Modified
05/07/03