CHARACTERISTICS IN LOW VOLTAGE I

Frequency ; the nominal frequency of the voltage supplied is 50 Hz normal operating conditions, the value
half of the fundamental frequency measured in periods of 10 s should be placed in the following ranges:
- Coupled network for synchronous connections to an interconnected system:

50 Hz ± 1% (ie 49.5 Hz to 50.5 Hz) for 99.5% a year
50 Hz +4% / - 6% (ie 47 Hz to 52 Hz) for 100% of the time

- No network connection to an interconnected system synchronous (eg food webs that exist in
certain islands):

50 Hz ± 2% (ie 49 Hz to 51 Hz) for 95% of one weeks
50 Hz ± 15% (ie 42.5 Hz to 57.5 Hz) for 100% of the time

Amplitude of the voltage supplied
A standard nominal voltage for low voltage general networks is A = 230 V, both phase-neutral
and between phases

- In the case of a three-phase 4-wire:
A = 230 V between phase and neutral;

- In the case of a three-phase 3-wire:
A = 230 V between phases.
NOTE In low voltage systems and the declared voltage rating equal.

Variations of the voltage supplied
Requirements
Voltage variations should not exceed ± 10%.
This excludes situations like that arise following faults or voltage interruptions, beyond the
reasonable control of the parties involved.

NOTE 1
Experience has shown that voltage deviations maintained within ± 10% over a long period of time are extremely unlikely, but theoretically could be within the limits given in paragraph 4.3.2. For this reason, in accordance with product standards and associated facilities and the application of IEC 60038, the end user's computers are usually designed to tolerate variations of ± 10% of the rated voltage of the system, which is enough to cover most of the conditions of supply. It is assumed that is neither technically nor economically feasible to have teams that are capable of working with voltages higher tolerances to ± 10%. If it were the case in which this occurs, the magnitude of the voltage supplied may deviate from this limit for a long period of time, additional measures should be taken in collaboration with the local network operator, depending on the risk analysis. The same applies in cases where specific devices have a sensitivity that increases with voltage variations.

NOTE 2
In case of electricity supply in remote areas with no long lines or a line connected to interconnected, the voltage may
be outside the range of +10% / -15%. Network users should be aware of the conditions.

Test Method
In normal operating conditions:
- For each period of a week, 95% of the effective values ​​of the voltage supplied averaged over 10 min
should be in the range of ± 10%, and
- All effective values ​​of the voltage supplied averaged over 10 min should be in the range A + 10% / -15%.

Fast voltage variations
Sporadic fast voltage variations
The rapid variations of the voltage supplied essentially from variations in load
facilities for users of the network or the network maneuvers.
In normal operating conditions, a rapid variation of the stress generally not exceeding 5% of A but, in certain circumstances, variations may occur which reach up to 10% of A for a short while, several times on the same day.
NOTE
A decrease in the tension that results in a voltage less than 90% of A is regarded as a voltage dip.

Flicker severity
In normal operating conditions for each period of one week, the level of severity of long duration
flicker due to voltage fluctuations should be Plt! 1 for 95% of the time.
NOTE
The flicker response is subjective and can vary according to the causes of perception and by duration. In some cases, Plt = 1 can
lead to trouble, while in other cases, higher levels of Plt not the cause.

Voltage dips
The voltage dips are generally caused by faults that occur on the premises of the users of the network or grid. These random events are fundamentally unpredictable. Its annual frequency depends mainly on the type of distribution network and the observation point. In addition, their distribution in a year can be very irregular.

Indicative values:
In normal operation, the expected number of voltage dips in a year can go a few tens to a thousand. The majority of voltage sags with a duration of less than a second and a voltage
than 40% residual. However, sometimes sags can occur from a depth and duration
superior. In some places, it often sags occur with a residual voltage between 85% and
90% of A, which are caused by load switching facilities of the network users.

Interruptions of the supply voltage
Indicative values:
During normal operation, the annual number of interruptions of the voltage supplied can
vary from several tens to several hundreds. The duration of approximately 70% of interruptions
may be less than 1 s.
NOTE
In some documents, it is considered that the duration of interruptions not exceeding 1 min. But sometimes systems are used
control with active run times up to 3 min, to avoid long breaks.

Long interruption of the voltage supplied
Accidental interruptions are generally caused by external causes or events that can not be prevented by the operator of the distribution network. It is not possible to indicate typical values ​​for the annual frequency and duration of long interruptions. This is due to considerable differences in the architecture of networks in different countries, as well as the unpredictable effects of adverse weather conditions and external causes.

Indicative values:
In normal operating conditions, the annual frequency of voltage dips exceeding 3 min
may be less than 10 or as high as 50, depending on the region.
Indicative values ​​of planned outages do not occur on the grounds that are announced in advance.

Temporary surges in the network between conductors and earth
A temporary surge in the frequency of the network is usually during a free kick in the overall network distribution or in a user facility and disappears at the time of disposal of such failure. Under these conditions, the voltage can reach the value of phase voltage (up to 440 V in networks
230/400 V), due to the residual voltage three-phase network, depending on the actual value of the degree of
load imbalance, and the impedance is maintained between the conductor and ground failure.
The length is limited by the time it takes the protection and medium voltage circuit breaker
clear the fault, usually not more than 5 s.
Under certain conditions, a failure that occurs upstream of a transformer can temporarily produce
overvoltages in the low voltage side for the duration of the fault current. Such surges do not exceed
usually 1.5 kV rms.

Overvoltages between live conductors and earth
The surge generally not exceed 6 kV (peak value).
NOTE 1
The rise time can vary from less than a few microseconds to several milliseconds. However, for physical reasons, the
longer duration transients typically have much lower amplitudes. Therefore, the coincidence of high amplitudes
with long rise times is extremely unlikely.

NOTE 2
The energy content of a surge varies considerably according to their origin. An induced voltage due to lightning is characterized by a higher amplitude and a lower energy content of an overvoltage caused by maneuvers, because the latter generally last much longer.

NOTE 3
Low voltage installations and equipment from end users are usually designed according to the Standard EN 60664-1, for withstand surges in most situations. When necessary, according to IEC 60364-4-44, should be selected protective devices shock waves, according to IEC 60364-5-53, to take into account the real situations. It is assumed that this would cover both induced overvoltages due to lightning as maneuvers.

Unbalance of the voltage supplied
In normal operating conditions for each period of a week, 95% of the effective values ​​averaged over 10 min from the reverse component (fundamental) of the supply voltage must be between 0% and 2% of the direct component (fundamental). In some areas where facilities for users of the network are partially monophasic or biphasic, imbalances can reach 3% in the three-phase supply points.
NOTE
This European Standard does not suggest any values ​​that correspond to the inverse of the stress component, which is essential for any damage to the equipment connected to the network.

Harmonic voltages
In normal operating conditions, during each period of a week, 95% of the RMS values ​​of each harmonic voltage averaged over 10 minutes must not exceed the values ​​given in Table 1. Elevated voltages to give a given harmonic may be due to resonances.
In addition, the rate of total harmonic distortion of the supply voltage (THD) (including all harmonics up
the order 40) should not exceed 8%.
NOTE
The limit of order 40 is by convention.

Posted in: Flicker severity,Test Method,Voltage dips