Time synchronization systems that utilize the global navigation satellite systems (GNSS) are widely used in the monitoring

control

and protection of transmission networks. They ensure that phasor measurement units (PMUs) can accurately monitor voltage phase angles

increase the accuracy of fault locators

enhance the capabilities of disturbance recorders

and allow differential feeder protection to use re-routable communication networks. However

concern about the reliability of GNSS receivers used in intelligent electronic devices (IEDs) have been reported; problems include mal-operations of differential protection

erroneous satellite timing/location messages

inappropriate installations

and blocking of satellite signals due to illegal use of GNSS jammers in vehicles. Utilities now require a timing system less dependent on the use of low cost GNSS receivers integrated into IEDs

but one that uses Grandmaster clocks

slave and transparent clocks

and an Ethernet communication network. The IEEE 1588-2008 synchronization protocol uses the Ethernet to disseminate a global time reference around a substation. A future substation will probably include duplicate 1588 grandmasters

each incorporating stable oscillators with GNSS and terrestrial receivers

in conjunction with a 1588 compliant Ethernet data network with slave and transparent clocks

and redundancy boxes for interfacing with IEDs. Although IEEE 1588 protocol is promising for future substation automation systems

its performance and impact has to be fully evaluated before it can be used in real substations. This paper describes how an IEEE 1588 time synchronization testbed is designed

constructed

and tested. Testing involves measuring the time offset when the Ethernet is heavily loaded with other traffic and the holdover capability of 1588 clocks. Additional delay introduced by IEEE 1588 traffic is also measured. As there is limited testing on GPS receivers within the power industry

this paper also uses the testbed to evaluate the steady state and transient behavior of GPS receivers. The results show a 1588 time synchronization system is accurate

secure

and ideally suited for protection and control applications

compared to a timing system merely based on GPS receivers. The information described in this paper should increase a utility's confidence in applying IEEE 1588 timing in a real substation.