EDC   5  (5235)   P3   
  
 
 
 
 
 
 
 
 
 
 
 
 
DRAFT  TANZANIA  STANDARD   
(Draft for comments only)  
 
Mini-Grid Systems  –  
 
Part 2:  Application  of Inverters   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TANZANIA  BUREAU  OF STANDARDS   
 
 
 
TBS 2017                                                                      
 
    
First Edition  2017    
 
Annex   A  Tests   Requirements   Definitions     
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9  T able of content   
 
1   
Scope ................................   
2  Normative   references   ................................   
3  Quality   Control ................................   
4  Environmental   Conditions   
5  Electrical   System   Parameters   ................................   
6  ................................   
7  ................................   
8  ................................   
9  ................................   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TANZANIA    STANDARD     
   0  Foreword    
 
This Draft  Tanzania  Standard  specifies  minimum  technical  requirements  for the design,   
manufacture,  test and supply  of Inverters  and their application  to mini-grid systems  used  in  
decentralized  rural electrification  for providing  safe energy  services  to consumers  . Modern   
mini-grids  may consist  of multiple  distributed  generators,  including  conventional  engine -  
generators,  photovoltaic  arrays,  wind turbines  and energy  storage  syste ms.  
 
This Draft  Tanzania  Standard  is part of an integrated  set of specifications  and standards   
issued  to govern  design  and construction  of mini-grid power  systems  in Tanzania.   The mini-  
grid standards  have  been  developed  to support  improved  residential,  commercial  and public   
services  for rural communities  in Tanzania.  These  mini-grid energy  systems,  when  properly   
designed,   will  support   affordable   and  reliable   energy   supply   for  remote   households,   
community  services,  commercial  and economic  activities  including  shops,  workshops,  micro -  
industry,  fresh  water  pumping,  secondary  schools,  health  services,  public  lighting,  places  of  
worship  or cultural  activities,  agro-processing  activities  and other  activities.     
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 This  standard   shall  be  read  in  conjunction   with  other   relevant   –  Tanzania   
specifications
  and  standards
  applicable
  Standards,
  1   Scope    
 
1.1   
This standard  covers  power  electronics  (primarily  inverters),  which  are used  to  
connect  distributed  generation  equipment  (specifically  photovoltaic  arrays  and  
battery  systems)  to mini-grid power  systems.   This standard  primarily  deals  with  
safety  in construction  and operation,  including  anti-islanding.   
 
1.2   
This standard  covers  all standalone  inverters,  grid-interactive  inverters  and multi-  
mode  inverters  used  in mini-grids  ranges  between  10 kW and 1MW  of total  
generating   capacity.     It  shall  be  noted   that  although   the  standard   applies   
specifical ly  to  power   electronics,   it  “touches   on”  issues   with  connected   
equipment,  including  wiring,  fault protection,  transformation  and grounding.   
 
1.3   
This standard  applies  to all inverters  used  in mini-grid systems  with total installed   
inverting  capacity  between  10 and 1,000kVA -ac.  Inverters  which  are individually   
of less than 10kVA -ac capacity  but are operated  in parallel  to achieve  a total  
installed   capacity   equal   to  or  greater   than  10kVA -ac  are  considered   to  be  
covered  by this standard.    
 
1.4   
 
 to  
compatibility  and standardization  in the distribution  system.     
 
have   
 
uniformity,   
 
 
2    
 
Normative    references       
 
For the purpose  of this Tanzania  standard,  the following  references  shall apply:   
 
IEC 62109 -1: 2010  Safety  of power  converters  for use in photovoltaic  power  systems  -  
Part 1: General  requirements   
 
IEC 62109 -2: 2011  Safety  of power  converters  for use in photovoltaic  power  systems  -  
Part 2: Particular  requirements  for inverters   
 
IEC 62116:  2014  Utility -interconnected  photovoltaic  inverters  - Test procedure  of  
islanding  prevention  measures   
 
IEC 61727:  2004  Photovoltaic  (PV) systems  - Characteristics  of the utility    
interface  in the event  of conflict  between  these  standards  and this specification,  this  
specification  shall govern   
 
 
 
3   
 
 
Terms  and definitions   
 
For  the  purposes   of  this  standard,   the  following   terms   and  definitions   shall  apply    
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 3.1 Islanding     
 
Continued  operation  of part of a distribution  grid after the primary  grid/mini -grid has  
experienced  failure.   
3.2 Intentional  Islanding    
 
Intentional  operation  of an electrical  island  which  has been  isolated  from the primary   
grid / mini-grid.  
3.3 Unintentional  Islanding     
 
Continued  unplanned  and unintended  operation  of one or more  distributed  generation   
sources   imparting  energy  to the primary  grid after it has failed  and is assumed  to be un-  
energized.   
3.4 Anti-Islanding       
 
A function  of a grid-interactive  inverter  which  is designed  to prevent  the continued   
existence  of an unintentional  island.   
3.5 Standalone  inverter   
 
An inverter  which  is not intended  to be connected  to a utility  grid, or which  forms  the  
sole generator  on a mini-grid.  Also referred  to as a “grid-forming”  inverter.   
3.6 Grid-interactive  inverter    
 
An inverter  which  is designed  to synchronize  to and exchange  power  with a utility  grid  
containing  additional  generation  sources.   Also referred  to as a “grid-following”  inverter.   
3.7 Multi -mode  inverter    
 
An inverter  which  may be connected  to the grid at times  but may also be capable  of  
operating  as a standalon e inverter.   
 
 
4    
 
Quality    Control    
 
The standalone  inverters,  grid interactive  inverters  and multi-mode  inverters  used  in mini-  
grids  shall be fabricated  in a plant  that has an established  and credible  past record  of  
production   of  similar   equipment   and  that  holds   an  ISO  9001   certification   for  quality   
management.    
 
 
5    
 
Environmental    Conditions    
 
Standalone  inverters,  grid interactive  inverters  and multi-mode  inverters  used  in mini-grids  
shall be labeled  for service  under  one of the following  conditions  (IEC 62109 -1):  
5.1 Outdoor   
 
The equipment  may be operated  fully or partly  exposed  to direct  rain, sun, wind,  dust,   
fungus,  ice, condensation,  radiation  to the cold night  sky and to the full range  of outdoor   
temperature  and humidity.   Wet location  requirements  apply.   
 
 
 
  
 0  0  0  0  0  0  5.2 Indoor,  unconditioned   
 
The equipment  is fully covered  by a building  or enclosure  to fully protect  it from rain,  
sun, windblown  dust,  fungus,  and radiation  to the cold night  sky, but the building  or  
enclosure  is not conditioned  in terms  of temperature,  humidity  or air filtration,  and the  
equipment  may experience  condensation.   If the equipment  is not rated  for wet location   
use, then the installation  instructions  shall specify  that the installation  location  must  be  
dry except  for condensation.   
 
 
5.3 Indoor,  conditioned   
 
The equipment  is fully covered  by a building  or enclosure  to fully protect  it from rain,  
sun, windblown  dust,  fungus,  and radiation  to the cold night  sky, and the building  or  
enclosure  is generally  conditioned  in terms  of temperature,  humidity  and air filtration.   
Condensation  is not expected.   If the equipment  is not rated  for wet location  use, then  
the installation  instructions  shall specify  that the installation   location  must  be dry,  
including  no expected  condensation.   
 
 
5.4 Specific  Requirements   
 
The specific  requirements  necessary  for meeting  the environmental  classifications   
shall be as follows:   
 
Table  1 – Nominal  values  for anti-islanding  protection   
 
Environmental  Conditions   
Rating   Outdoor   Indoor,  unconditioned   Indoor,  conditioned   
Pollution  Degree   Min PD3  Min PD3  Min PD2  
 
Wet Location    
Yes   
No   
No  
 
Ingress  Protection    
Min IP34   
Min IP20   
Min IP20  
 
Ambient  Service  Temp    
-20 C to +50 C   
-20 C to +50 C   
+0  C to +40 C  
 
 
Ambient  Humidity  Range    
 4% to 100%   
(Condensing)    
 5% to 95%  
Non-condensing    
 5% to 95%  
Non-condensing   
 
UV Exposure    
Required    
Not required    
Not required   
 
 
 
6    
 
 
Electrical    System   Parameters    
 
System  parameters  of mini-grids  for low voltage  power  distribution  networks   are as follows:   
 
a)  Nominal  system  low voltage  (U): 230/400V  (±10%)    
b)  Maximum  permissible  system  low voltage  (Um):   253/440  V   
c)  Minimum  permissible  system  low voltage :   215/374  V   
d)  System  frequency:  50 Hz  
e)  Neutral  grounding  arrangement:  multi-grounded   
f)  Single  or three  phase  configurations:  allowed   
 
  
 i)  
j)  f)  7   Requirements    
7.1  Construction   
 
Construction   should   follow   IEC  62109   Parts  1  and  2  including:    
 
a)  Marking  (section  5)  
b)  Environmental  (section  6)  
c)  Protections  against  shock  and electrical  hazards  (Section  7)  
d)  Protection  against  mechanical  hazards  (Section  8)  
e)  Protection  against  fire hazards  (section  9)  
 Protection  against  sonic  pressure  hazards  (Section  10)  
g)  Protection  against  liquid  hazards  (Section  11)  
h)  Chemical  Hazards  (Section  12)  
 General  physical  requirements  (Section 13)  
 Components  (Section  14)  
k)  Software  and firmware  performing  safety  functions    
 
It shall be noted  that although  Section  14.8 addresses  batteries,  this is only for batteries   
that are a direct  part of the power  electronics  equipme nt.  
 
 
8    
 
Tests    
8.1  General  Testing   
 
8.1.1    
Anti-islanding  Testing   
 
Testing   of  anti-islanding   circuits   shall  be  performed   as  specified   in  IEC  62116.    
8.1.2   Anti-Islanding  Set Points   
 
The  nominal   values   for  anti-islanding   protection   are  as  follows:    
 
 
Table  1 – Nominal  values  for anti-islanding  protection   
 
Parameter    
Max.  Clearance  time*     
Trip setting    
Over voltage  (level  2)   0,05s   230V  +35%  (311V)    
Over voltage  (level  1)   2,0s  230V  +4,3%  (240V)    
Under  voltage  (level  1)   2,0s  230V  -13% (200V)    
Under  voltage  (level  2)   0,1s  230V  -50% (115V)   
Over frequency    0,1s  50Hz  +2% (51,0Hz)    
Under  frequency    0,1s  50Hz  -2% (49,0Hz)    
Reconnection  time   At least 120s  
Permanent  DC-injection   0,5%  of rated  inverter  output  current    
Loss of main  IEC 62116    Inverter  shall detect  and disconnect  within  0,3s   
 
 
The  trip  setting   values   and  clearance   times   shall  be  adjustable   by  a  qualif ied  user  
and  may  be  relaxed   up  to  the  followi   ng  table  to  ensure   proper   operation   on  a  mi  ni  -   
grid.    If  setti  ngs  are  changed   from  the  nominal,   this  must  be  documented   and  kept  i  n   
 
 
 
  
 a  secure   location   near  the  i  nverter   and  with  other   maintenance   documents.     (Ref  
Annex   A)   
 
Table  2 – Maximum  permissible  values  for anti-islanding  protection   
 
Parameter    
Max.  Clearance  time*     
Trip setting    
Over voltage  (level  2)   0,2s  230V  +35%  (311V)    
Over voltage  (level  1)   5,0s  230V  +4,3%  (240V)    
Under  voltage  (level  1)   30,0s   230V  -13% (200V)    
Under  voltage  (level  2)   1,0s  230V  -50% (115V)   
Over frequency    10,0s   50Hz  +5% (52,5Hz)    
Under  frequency    10,0s   50Hz  -10% (45,0Hz)    
Reconnection  time   At least 30s  
Permanent  DC-injection   0,5%  of rated  inverter  output  current    
Loss of main  IEC 62116    Inverter  shall detect  and disconnect  within  0,3s   
 
It  is  recommended   that  mi  ni-grid  operators   check   for  proper   anti-islanding   when   the  
system   is  commissioned   and  whenever   set-point    values   are  changed   or  i  nverter    
firmware   is  updated.   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 Annex   A   
 
                (normative)    
 
Inverter   Anti-Islanding   Set  Point   Form    
 
System  Description    
[insert  sys description  and location  here]   
Reason  for test  [commissioning,  addition  of generation,  etc.]  
Date of Test  [insert  date here]   
Result  of test  [pass,  fail, comments]   
Parameter   Max.  clearance  time*    Trip setting    
Over voltage  (level  2)   X s   230V  Y% (XXX  V)   
Over voltage  (level  1)   X s   230V  +4,3%  (XXX  V)   
Under  voltage  (level  1)   X s   230V  -13% (XXX  V)   
Under  voltage  (level  2)   X s   230V  -50% (XXX  V)  
Over frequency    X s   50Hz  +X% (XXX  Hz)   
Under  frequency    X s   50Hz  -X% (XXX  Hz)   
Reconnection  time   at least X s   
Permanent  DC-injection   0,5%  of rated  inverter  output  current    
Loss of main  IEC 62116    Inverter  shall detect  and disconnect  within  X s