IEEE Power & Energy Magazine - September/October 2015 - 63

dispatching digital network (SPDnet) demand high reliability, real-time responsiveness, and safety. This requires
guaranteeing key performance requirements such as
network time delay and convergence time. Currently, in
accordance principles developed for dual independent
backbone networks and multiple layers of integration,
a unique data dispatching network is applied, based on
exclusive channels (combining a synchronous digital hierarchy, Internet protocols, and optical fiber) using the URL
stratification structure and alternate route functions. The
network utilizes highly reliable core equipment, together
with double master controls. A three-level border gateway protocol route is used to realize a multiprotocol
label-switching virtual private network, through which
different types of network tasks can be isolated and the
safety of dispatching tasks can be maintained. A quality
of service strategy is employed to ensure that transmission bandwidth and real-time demand of data flow are met
for important tasks.
For data synchronization, SDPnet is designed as a threelayer structure: a core layer, a backbone layer, and an integration layer. The core layer consists of state, backup, and
regional dispatching centers, along with a few related provincial ones. The backbone layer contains the majority of
provincial dispatching center nodes. The integration layer
includes directly dispatched power plants, substations, and
converter stations.
Several national standards have been established for realtime data application in power systems, including DL/T 4762012 for real-time data communication among dispatching

Over Ten
Ten Years
Years
Over
0.77%
0.77%

Under One Year
12.01%

Six
Six
to Ten Years
18.58%
18.58%

One to Five Years
68.63%

figure 2. Distribution of PMUs over 110 kV by operation
duration.

centers, DL/T 634/5 (104) for real-time data communication
between a central station and substations, and DL/T 860 7-2
(which is IEC 61850 compatible) for data communication
within a substation. In addition, IEEE standard C37.118 is
used for PMU/WAMS phasor data communication.
Time-synchronization management is another critical infrastructure for PMU/WAMSs. For this, the BeiDou
navigation satellite system provides the main time clock
source, with accuracy of 20-100 ns. The Global Position
System serves as the auxiliary clock source, with accuracy
of 6-12 ns, while synchronous digital hierarchy offers a
further backup solution. A hierarchical management system is implemented for monitoring time synchronization

Control-Center
PDC
Control-Center Side
Substation Side
Gateway

Station-Level
Devices

Monitoring
Panel

PDC

Station Level

Bay Level

Gateway

Firewall

IED

PMU

IED

Other IEDs

Process Level
Merging
Unit

Switchgear
Control Unit

Security
Zone I

Security
Zone II

figure 3. PMU functions in a smart substation. PDC: phasor data concentrator; IED: intelligent electronic device.
september/october 2015

ieee power & energy magazine

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2015