UCTE

The "Union for the Co-ordination of Transmission of Electricity" (UCTE) is the association of
transmission system operators in continental Europe, providing a reliable market base by
efficient and secure electric "power highways".
The UCTE (up to the 30th of June 1999 named UCPTE) has created a “Survey of essential
UCPTE recommendations for the interconnected operation” (dated 31st of December 1991)
and important additional rules and recommendations on specific subjects after that date. Up
to now (and if not already replaced by the Operation Handbook) these documents have been
in force in the UCTE.
The “UCTE Operation Handbook” (OH) is an up-to-date collection of operation principles
and rules for the transmission system operators in continental Europe. Additional references
to UCTE operation and security rules and recommendations as well as a list of publications,
public statistics and information about the members, organisation, structure and activities of
the UCTE in general can be found on the UCTE Web site:
!http://www.ucte.org
This introduction is the cover paper for the operation handbook policies and appendices. It
includes a general overview, the main characteristics and scopes of the handbook, a
description of the handbook structure with the table of contents as well as guides and
descriptions for readers. The glossary of terms is provided in a separate paper.

LOAD-FREQUENCY CONTROL
AND PERFORMANCE

Introduction
The objective of PRIMARY CONTROL is to maintain a balance between GENERATION and
consumption (DEMAND) within the SYNCHRONOUS AREA, using turbine speed or turbine
governors. By the joint action of all interconnected undertakings / TSOs, PRIMARY CONTROL
aims at the operational reliability of the power system of the SYNCHRONOUS AREA and
stabilises the SYSTEM FREQUENCY at a stationary value after a disturbance or incident in the
time-frame of seconds, but without restoring the reference values of SYSTEM FREQUENCY and
power exchanges (see !P1-B for SECONDARY CONTROL). Adequate PRIMARY CONTROL
depends on generation resources made available by generation companies to the TSOs.
Please refer to appendix 1 (see !A1-A) for basics and principles of PRIMARY CONTROL.
This policy section replaces the corresponding sections for primary control in the latest
“UCPTE-Ground Rules concerning primary and secondary control of frequency and active
power within the UCPTE”, dated 1998.
Criteria
C1. Nominal frequency. The set-point frequency (or scheduled frequency) f0 (see !P1-
D) defines the target value of the SYSTEM FREQUENCY f for system operation. Outside
periods for the correction of SYNCHRONOUS TIME (see !P1-D), the nominal frequency
value in the SYNCHRONOUS AREA is 50 Hz.
C2. Frequency deviations. A FREQUENCY DEVIATION Δf (the departure f–f0 of the actual
SYSTEM FREQUENCY f from the scheduled frequency f0) results from a disturbance or
an incident and may occur during normal system operation. Different criteria are used
to distinguish the size of this deviation:
C2.1. Calling up of Primary Control. To avoid calling up of PRIMARY CONTROL in
undisturbed operation at or near nominal frequency, the FREQUENCY DEVIATION
should not exceed ±20 mHz. PRIMARY CONTROL is activated if the FREQUENCY
DEVIATION exceeds ±20 mHz (the sum of the accuracy of the local frequency
measurement and the insensitivity of the controller, see !P1-A-R1 and !P1-
A-R2).
C2.2. Maximum Quasi-Steady-State Frequency Deviation. The quasi-steady-state
FREQUENCY DEVIATION in the SYNCHRONOUS AREA must not exceed ±180 mHz
(maximum permissible steady-state FREQUENCY DEVIATION; under the condition
of SELF-REGULATION OF THE LOAD according to !P1-A-C4).
C2.3. Minimum Instantaneous Frequency. The instantaneous frequency must not
fall below 49.2 Hz (that corresponds to -800 mHz as maximum permissible
dynamic FREQUENCY DEVIATION from the nominal frequency !P1-A-C1) in
response to a shortfall in generation capacity equal to or less than the
reference incident according to !P1-A-C3.
C2.4. Load-Shedding Frequency Criterion. LOAD-SHEDDING (automatic or manual,
including the possibility to shed pumping units) starts from a SYSTEM
FREQUENCY of 49.0 Hz (or below). The detailed step-plans for LOAD-SHEDDING
(in the responsibility of the TSOs, with the possibility to perform earlier
shedding of pumping units at higher frequency value as an operational
measure, with the lowest value of 47.5 Hz and the need of progressive stages
in between) define additional frequency criteria for further measures.
C2.5. Maximum Instantaneous Frequency. The instantaneous frequency must not
exceed 50.8 Hz (that corresponds to +800 mHz as maximum permissible
dynamic FREQUENCY DEVIATION from the nominal frequency !P1-A-C1) in
response to a loss of load or interruption of power exchanges equal to or less
than the reference incident according to !P1-A-C3.

C3. Reference Incident. The maximum instantaneous deviation between generation and
demand in the SYNCHRONOUS AREA (by the sudden loss of generation capacity, loadshedding
/ loss of load or interruption of power exchanges) to be handled by PRIMARY
CONTROL starting from undisturbed operation depends on the size of the area / zone1
and on the size of the largest generation unit or generation capacity connected to a
single bus bar located in that area2.
C3.1. First Synchronous Zone. For the first synchronous zone as in 2003 the
maximum power deviation to be handled is 3000 MW, assuming realistic
characteristics concerning system reliability and size of loads and generation
units.
C3.2. Second Synchronous Zone. For the second synchronous zone as in 2003,
the maximum power deviation to be handled is 540 MW.
C3.3. Other Synchronous Areas. For other SYNCHRONOUS AREAS (UCTE
SYNCHRONOUS AREAS), that are not connected to the main synchronous zone,
the size of the reference incident needs to be defined in each particular case
with respect to the size of the area and the size of the largest generation units
located in that area.
C3.4. Observation Incident. Incidents, such as the sudden loss of generation or
load, that exceed 1000 MW in the first synchronous zone or 250 MW in the
second synchronous zone are considered to be relevant for system
observation in that zone3.
C4. Frequency Characteristics. Key values of the frequency characteristics are defined
on the basis of system observation4.
C4.1. Self-Regulation of Load. The self-regulation of the load in all SYNCHRONOUS
AREAS is assumed to be 1 %/Hz, that means a load decrease of 1 % occurs in
case of a frequency drop of 1 Hz.
C4.2. Security Margin. For FREQUENCY CONTROL, a static security margin of 20 mHz
is defined, identical with the calling up of PRIMARY CONTROL (see "P1-A-C2.1).
C5. Deployment Times of Primary Control Reserve. The time for starting the action of
PRIMARY CONTROL is a few seconds starting from the incident, the deployment time for
50 % or less of the total PRIMARY CONTROL RESERVE is at most 15 seconds and from
50 % to 100 % the maximum deployment time rises linearly to 30 seconds.
C6. Frequency Change Indicators. For special use in a post-operation analysis, the
following criteria are defined to measure the characteristics of absolute changes of the
SYSTEM FREQUENCY within a short period of time.
C6.1. Periods of Time. Typical periods of time are ±60 minutes, ±15 minutes and
±5 minutes around the time of an incident or the change of the hour.
1: The definitions of synchronous zones (first and second zone as existing today as a result of the
Balkan war) are temporal only due to the planned reconnection of the UCTE area. The reconnection is
scheduled for 2005. The system load for the first SYNCHRONOUS AREA typically varies between 150 GW
off-peak and 300 GW peak.
2: The final values used in the definition of the reference incidents are determined by the UCTE SG
“TSO-Forum” and finally confirmed by the UCTE WG “Operations and Security” and the UCTE SC. The
values given are under consideration.
3: The values have been adapted by the UCTE SG “TSO-Forum” in 2001 and are reviewed annually.
4: The final values used in the definition are determined by the UCTE SG “TSO-Forum” and finally
confirmed by the UCTE WG “Operations and Security” and the UCTE SC. The values given are under
consideration.
C6.1. Periods of Time. Typical periods of time are ±60 minutes, ±15 minutes and
±5 minutes around the time of an incident or the change of the hour.
C6.2. Maximum Time Grid. The values used for frequency change indicators are
based on a maximum time grid of 10 seconds.
C6.3. Frequency Patterns. Typical patterns of the frequency within a short period of
time can be: constant with / without offset, decrease, increase, peak up, peak
down, peak up down and peak down up.
C6.4. Peak Frequency Range within Period. The peak frequency range is
calculated as the difference between the maximum and the minimum
frequency within the given period of time.
C6.5. Peak Frequency Derivative within Period. The peak frequency derivative is
determined as the maximum or minimum derivative of the frequency within the given period of time.