H. Eslava et al.
Tele-Protection in Electric Substations
At present, electrical energy companies focus on the potential risks of using non-deterministic Ethernet to
transmit protection signaling at substations. This may cause failure in electrical supply systems, leading to volt-
age sags or service interruptions that have a negative impact on every-day-life activities and, to a worse extent,
have serious financial consequences.
The main purpose of protection systems is to quickly isolate (take out of service) from the system any piece of
high-power equipment that shows faulty behavior. Likewise these protection systems must limit the extent of
damage caused to equipment and disconnect the faulty equipment as quickly as possible in order to keep stabil-
ity and preserve the good condition of the whole power system. Since transient stability is closely related to the
capabilities of the power system to maintain synchronization when undergoing massive perturbations, satisfac-
tory behavior of protection systems is important in order to ensure stability.
In order to serve its purpose, a protection system must be capable of detecting variations that may occur
around a given equilibrium point, reducing uncertainty and undefined states as much as possible. Such a system
should also detect anomalies in specific components or pieces of power equipment as well as and limiting the
time span of any anomaly (minimizing undesired delays). In conclusion, protection must contribute to the fol-
lowing desired features: 1) availability (% of time estimated for equipment, or parts of the power system, to op-
erate properly and be fully available), 2) reliability (probability that a piece of equipment, or part of the system,
is fully operational with no failure events within a given time span) and 3) instability (ability to recover a previ-
ous operation state as a synchronous operation of generators after disturbances) [4].
Classification of different types of protection falls into three main groups. The first group corresponds to
transmission-line protection, where the following devices are used: over-current breakers (either time-set or in-
stant-response, directional, non-directional, or directional with communication capabilities), differential line
breakers and distance breakers (with or without communication). The second group corresponds to distance
breaker protection, which is normally installed in places where failure-isolation instantaneous response times are
set. This second group allows larger instantaneous operation zones, greater sensitivity, easy adjustment, easy
coordination, and offers particular advantages such as remaining unaffected by configuration changes in the
power system. Lastly, the third group corresponds to power oscillation protection. This type of protection pro-
vides a balance between what is generated and what is consumed in terms of active and reactive power. Within
an electrical power system, in stationary regime, any change in either the generated, the power demand, or in the
electrical system itself, causes changes in the corresponding power transfer, which in turn oscillates until reach-
ing a new equilibrium point between the generation system and the load.
Typical power system response to disturbances depends on configuration and also on the extent of perturba-
tions. Depending on the type of disturbance as well as on the counteractions of protection equipment and control
systems, electrical systems may remain stable and continue their normal operation around a new equilibrium
point. This type of oscillation is referred to as stable-power oscillation. In case of system instability due to dis-
turbances, a separation of rotor angles occurs in some generators, accompanied by power oscillations that lead to
synchronization losses among generators (or among interconnected systems). This type of oscillation is called
instable power oscillation [5].
3. Laboratory Equipment and Application
Considering the aforementioned conceptual framework as well as the operation of Metro-Ethernet networks, the
structure of standard IEC61850 and IEEE 1588 precision time protocol and the benefits of applying tele-protec-
tion; the following section describes the equipment that constitutes a complete laboratory installed at the facili-
ties of Openlink in Bogotá (Colombia). The main laboratory components are the following:
3.1. CISCO ME 3400 Series Ethernet Access Switches
Built for service providers, these multilayer customer-located switches allow you to deploy Ethernet-to-the-
home (ETTH) “triple play” services and Ethernet-to-the-business (ETTB) VPN services. Based on today’s most
widely deployed access switches, the Cisco Catalyst 2950 and 3550 Series, the Cisco ME 3400 Series provides
service-provider-friendly hardware and mission-specific software [6] a single ETTH and ETTB access solution
to help reduce total ownership costs and operating expenses, compact form factors for ease of deployment, only