Values of average phase voltages in settable aggregation period for voltage peak and minimum calculation are available as COSEM objects. Values in those objects are refreshed at the end of the measurement period and the same values are kept until the next period ends.
Vector registration method (∑L)
By vector method the vectors of each phase L1, L2 and L3 are summed:
– When the vector sum of energies is positive, the meter registers A+ energy.
– When the vector sum of energies is negative, the meter registers A- energy.
Example (same load in each phase)
Total registration: OBIS 22.214.171.124.0 = (A+) + (A-) + (A+) = A+
Arithmetic registration method
The meter can register A+ and A- energy at the same time with the arithmetic registration method.
Example (same load in each phase)
Total registration, import (forward) direction: OBIS 126.96.36.199.0 = (A+) + (A+)
Total registration, export (reverse) direction: OBIS 188.8.131.52.0 = (A-)
Absolute registration |A |
The registration of absolute active energy |A| is as follows:
Example (same load in each phase)
Total registration, import direction: OBIS 184.108.40.206.0 = |A+| + |A-| + |A+|
With this settings the meter registers only forward energy.
If the meter is tampered the display shows a raised hand ✋ and the internal relay disconnects the power supply. In this case the customer needs to apply for a tampering clearance token with the utility or the local Power Vending Center (POS). After the token is successfully entered the meter will close the relay and return to normal operation.
The Vending Center (POS, point of sales) produces a 20 digits transfer code (Token) generated based on user’s meter number and purchase amount. After the user input this code via the meter’s keypad, the meter will decrypt the code.
After passing the encryption authentication, the purchased energy amount is stored into meter’s memory and added to the available credit. (see meter feedback here)
If the customer has allowance to use emergency credit (overdraft), this energy amount is deducted from the new purchase amount. When the user is consuming energy, the meter deducts the credit according to the consumption.
Once the credit is zero or on emergency credit level, the meter disconnects the customer from power supply.
The example shows the information shortcode (07)1, the remaining credit (0.00) and the symbol that the relay has opened.
The principle of electrical energy measurement is to detect the actual current, the actual voltage and the phase shift (power factor). This values are giving us the instantaneous power . The power multiplied by the time is the consumed energy.
Let’s take a look at a terminal block for a direct connected threephase 4 wire meter.
The red arrows are indicating the so-called “I-P links”, one for each phase. By unfastening the two screws the link can be moved to the right side. So there will be no connection between the current- and voltage measurement circuits. This links are only for meter testing purpose with a test bench, as here the voltages and currents are provided individually. (The voltages are connected to the screw on the right side of the link.)
A meter in the field must have all links closed.
Phase current is measured and presented in corresponded DLMS/COSEM objects for each phase separately. Internally currents are always measured in mA.
Instantaneous current is measured in the meter every second.
A latching relay keeps its contact position indefinitely without power applied to the coil. The advantage is that the coil consumes power only for an instant moment while the relay is being switched, and the relay contacts retain this setting across a power outage.
Usually in electricity meters the load switch is a latching relay.
It is located between the supply input and load output terminals of the energy meter.
The relay is able to make, carry and break all values of currents between the minimum switched current rating to the rated breaking current for all values of the rated operating voltage range and the specified operating temperature range of the meter.
For prepayment meters (see also IEC 62055-31)
The rated breaking current (Ic) shall be equal to Imax of the payment meter.
The minimum switched current shall be equal to the nominal starting current of the payment
The rated breaking voltage (Uc) shall be equal to the upper limit of the extended operating voltage range of the payment meter.
The load switches have different categories for utilization. (UC = Utilization Category)
The payment meter load switching utilization category is subject to the purchase agreement between the payment meter supplier and the purchaser and shall be marked on the label of the payment meter as UC1, UC2, UC3, or UC4.
Category UC1 is applicable to payment meters rated at maximum currents up to 100 A. There is no requirement for the load switch to also switch the neutral circuit. The short time overcurrent is acc. to IEC 62053-21 for meters for direct connection (30* Imax for half cycle).
Payment meters with load switching category UC2, UC3 or UC4 shall have the following properties:
a) capable of making and breaking negligible currents of specified values
b) capable of making, breaking and carrying rated currents of specified values
c) capable of making into fault currents with specified value and under specified conditions
d) capable of carrying short-circuit currents of specified value for a specified time period and under specified conditions
e) not required to provide safety isolation properties in the open contact position. These are requirements for the installation mains isolation switch
f) not required to break overload currents or short-circuit currents. These are requirements for fuses and circuit breakers that are normally used to protect the installation.
Fault current making capacity, C.5
Short-circuit current, C.6 test 1
C.6 test 2
For detailed information refer to IEC 62055-31, annex C.
Magnitude of last voltage sag
In this objects are the magnitudes of the last sags recorded.
Each detected voltage sag on specific phase voltage results in increment of corresponding phase voltage sag counter. The counter for any phase voltage sag is only incremented when all phase voltages come out of voltage sag condition.
Information on voltage magnitude for last occurred voltage sag on specific phase is stored in corresponding register object. For each phase meter records the minimum value of instantaneous phase voltages during voltage sag condition on that specific phase. The any phase voltage sag magnitude is registered when all phase voltages come out of voltage sag condition. The registered magnitude is the minimum measured instantaneous voltage in any phase during any phase voltage sag condition. With each new occurrence of specific voltage sag, previous voltage sag information is rewritten with new information.
In parallel with voltage sag magnitude, also voltage sag duration is recorded (per specific phase and for any phase). Duration records the time from the point that voltage level drops below voltage sag threshold to the point when it rises above voltage sag threshold including 2% hysteresis.
|Magnitude of last voltage sag||32.34.0||52.34.0||72.34.0|
Magnitude of last voltage swell
Each detected voltage swell on specific phase voltage results in increment of corresponding phase voltage swell counter. The counter for any phase voltage swell is only incremented when all phase voltages come out of voltage swell condition.
Information on voltage magnitude for last occurred voltage swell on specific phase is stored in corresponding register object. For each phase the meter records the maximum value of instantaneous phase voltages during voltage swell condition on that specific phase. The any phase voltage swell magnitude is registered when all phase voltages come out of voltage swell condition. The registered magnitude is the maximum measured instantaneous voltage in any phase during any phase voltage swell condition.
With each new occurrence of specific voltage swell, previous voltage swell information is rewritten with new information.
In parallel with voltage swell magnitude, also voltage swell duration is recorded (per specific phase and for any phase). Duration records the time from the point that voltage level rises above Vv_swell to the point when it drops below Vv_swell including 2% hysteresis.
Magnitude of last voltage swell
Maximum demand registers are storing the highest actual average value measured in each period. At the end of each period the actual average value from 1.0.x.4.0 registers are compared with the maximum demand value. If the actual average demand value is higher than the maximum demand value, it replaces the value stored in the maximum demand register.
Maximum demand values are set to zero value at the end of each billing period.
Maximum demand can be calculated for:
– active energy in both directions
-reactive energy per quadrant and as sum of two quadrants
– apparent energy in both flow directions
The tariff 1…8 is indicated by i.
The following meter-specific tokens are used:
General token handling
During input the numbers entered are displayed on the LCD, scrolling from right to left, with a dash displayed at every fourth digit. A counter in the upper left corner shows the total number of entered digits.
In this example 15 digits have already been entered.
The delay for accepting an input of the next digit is 20 seconds. After that time the display returns to the default display and the token entry was incomplete.
After token input the display shows one of the following information for 3 seconds.
The Token is accepted and the purchased energy amount is added to the remaining credit.
After that the meter shows the purchased amount for 5 seconds.
If the input is wrong, or random numbers are input with the purpose of tampering, the LCD display will indicate Reject-x, x is the times of wrong input.
In this example have been already eight inputs wrong. After 3 wrong inputs the keyboard is locked for 10 seconds. During that time the display shows: REJECT and the remaining waiting time in seconds (toggles every two seconds). With each new wrong input the lockout time for the keyboard is doubled. After 10 wrong inputs the customer needs to wait 1,280 seconds. This is the maximum waiting time. Each new incorrect input leads to another waiting time of 1,280 seconds. When token entry lockout is active the interface does not decrypt any meter specific tokens. Non-meter specific tokens and codes are still accepted and processed as normal while in lockout mode. The lockout period is reset to its original non-lockout status after any meter specific token has been successfully accepted by the meter or after meter is powered down and up again.
A security feature built into the STS is that no credit token can be used more than once. This is achieved by having an identifier built into the token. These identifiers are stored in a table in the meter, and the identifier of a new token is compared with the table If it has already been entered into the meter, the token will be rejected. The meter will give a notification that the token is used.
Due to the nature of the token identifier, an STS token has an effective life-time of approximately three months. If a token older than three months is entered, the meter may reject that token, and give an indication on the display that the token is old.
Full: A meter has a maximum amount of credit that it can store. If the number of units on the token will cause the meter credit to exceed this maximum value, the token will be rejected. The token may be entered at a later date when the level of credit in the meter has reduced enough to accept this token. The meter gives an indication that it is full.
OBIS stands for OBject Identification System
The load threshold can be changed by this token. If the user has an increased load demand that causes a frequent overload condition he needs to apply for a higher load threshold. A new Maximum Power Load Token will set this threshold.
This tokens are generally defined and are working with all STS prepayment meters. Sometimes this token are also called engineering token.
Internal Latching Relays Test
0000 0000 0001 5099 7584
0000 0000 0001 6777 4880
Total Units Register Value
0000 0000 0002 0132 8896
Key revision No. KRN
1844 6744 0738 4377 2416
3689 3488 1475 5332 2496
Power limit Threshold
0000 0000 0012 0797 4400
Actual active power
0000 0000 0044 2920 8064
Meter Software Version
0000 0000 0087 2419 5840
0000 0000 0022 8172 8512
Phase Power Unbalance Limit
0000 0000 0173 1410 5857
0000 0000 0688 5369 7029
Run all above Token in Sequence
5649 3153 7254 5031 3471
In a test sequence (run all), each test has a duration of 2.5 seconds, and is performed in the above order. For a single test per token, the test has a duration of 5 seconds.
After completion of the test sequence the meter returns to its actual operation mode.
Under-voltage / over-voltage
The meter detects condition when phase voltage rises above or drops below certain threshold levels. Such conditions are categorized as over-voltage or under-voltage. From samples of phase voltages the meter calculates the average values over a time period. This time period is synchronized with the meter clock. At the end of time period, each value of average phase voltage is compared to the over-limit and under-limit threshold parameters. When specific phase voltage value rises above over-limit threshold, an event for voltage over-limit is generated. Also when certain phase voltage drops below under-limit threshold, an event for voltage under-limit is recorded.
The meter also records end of voltage under/over limit condition (voltage normal event) when phase voltage returns between the two threshold levels. In order to prevent several events when phase voltage is exactly on the level of thresholds, a 2% hysteresis is implemented. This means that in order to detect normal voltage, phase voltage must rise additional 2% above parametrized under-limit threshold, or drop additional 2% below parametrized over-limit threshold.
Threshold for voltage over-limit
Time threshold for voltage over-limit
Threshold for voltage under-limit
Time threshold for voltage under-limit
Recorded when the duration is more than 1 minute.
Level 1: > +10%
Level 2: between +10% and +5%
Level 3: between +5% and 0%
Level 4: between 0% and -5%
Level 5: between -5% and -10%
Level 6: between -10% and -15%
Level 7: < -15%
When the rms voltage is below the nominal voltage by 10% to 90% for 0.5 cycles to 1 minute this event is called a sag.
Voltage sag starts when instantaneous voltage of specific phase drops below the threshold for Voltage Sag for longer than the time set. Voltage sag ends when the same instantaneous voltage rises above threshold for Voltage Sag.
Voltage sag detection involves 2% hysteresis, which means that once voltage drops below threshold , it must rise 2% above threshold in order to come out of voltage sag condition. The following information is recorded when voltage sag is detected:
- voltage sag counter is incremented by 1
- magnitude of voltage sag is stored
- duration of voltage sag is stored
- event is recorded in Power Quality Log
The threshold is defined as percentage of nominal voltage.
Time threshold for voltage sag specifies the required duration in seconds for which specific voltage must drop below voltage sag threshold until voltage sag condition is triggered.
|Magnitude for voltage sag||12.34.0|
|Counter for voltage sag||12.32.0|
When the RMS voltage exceeds the nominal voltage by 10 % to 80 % for 0.5 cycles to 1 minute, the event is called a “swell”.
Voltage swell starts when instantaneous voltage of specific phase rises above the threshold for longer than the time set in time threshold.
Voltage swell ends when the same instantaneous voltage drops below threshold. Voltage swell detection involves 2% hysteresis, which means that once voltage rises above threshold, it must drop 2% below in order to come out of voltage swell condition. The following information is recorded when voltage swell is detected:
- voltage swell counter is incremented by 1
- magnitude of voltage swell is stored
- duration of voltage swell is stored
- event is recorded in Power Quality Event Log
The threshold is defined as percentage of nominal voltage.
Time threshold for voltage swell specifies the required duration in seconds for which specific voltage must rise above until voltage swell condition is triggered.
|Magnitude for voltage swell||12.38.0|
|Over limit duration||12.37.0|
|Counter for voltage swell||12.36.0|