We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
[bug] __format_version__ not increased.
### Issue Description

The `__format_version__` in `_version.py` has not been increased eventhough the format got changed!

This is an issue in the develop branch **not** in master!

In my fork I made an update to many test cases since I changed the format, so I saved many networks in as files, they contain the current format_version (2.14.0). After merging the current version of develop I got some tests that suddenly failed eventhough my code should not mess with them. So I did a little diging and found that the expected and actual results differ in `net.res_switch_est` DataFrame. This is because the expected result only contains the old columns while the actual result contains the updated columns.

This is because the expected results are loaded form file using the `pandapower.from_json` function and since then format version is the same as the current format verison in `_version.py` the conversion to the newest format is not done. So the network is returned as loaded from file.
The actual results however are a product of a conversion from a different network type. So they are the output of a converter that creates a new pandapowerNet. These then contain all new columns.

If new columns are added `__format_version__` should be incremented at least in the bugfix number. But I would expect that this constitutes at least a minor release as a new format version most likely breaks backwards compatibility. On a bugfix version I would expect I go backwards and forwards without issue. But this is not the case if the format version changes! A 2.13.1 Network should sucessfully load on 2.13.0 but this will not work if new columns are added. So this change should be reflected by an increase of the format verison to at least 2.15.0 in my opinion.

The breaking commit is 516f8af as it changed the format without changeing the format version.


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `pandapower/_version.py`
Content:
```
1 import importlib.metadata
2 
3 __version__ = importlib.metadata.version("pandapower")
4 __format_version__ = "2.14.0"
5
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/pandapower/_version.py b/pandapower/_version.py
--- a/pandapower/_version.py
+++ b/pandapower/_version.py
@@ -1,4 +1,4 @@
 import importlib.metadata
 
 __version__ = importlib.metadata.version("pandapower")
-__format_version__ = "2.14.0"
+__format_version__ = "2.15.0"

{"golden_diff": "diff --git a/pandapower/_version.py b/pandapower/_version.py\n--- a/pandapower/_version.py\n+++ b/pandapower/_version.py\n@@ -1,4 +1,4 @@\n import importlib.metadata\n \n __version__ = importlib.metadata.version(\"pandapower\")\n-__format_version__ = \"2.14.0\"\n+__format_version__ = \"2.15.0\"\n", "issue": "[bug] __format_version__ not increased.\n### Issue Description\r\n\r\nThe `__format_version__` in `_version.py` has not been increased eventhough the format got changed!\r\n\r\nThis is an issue in the develop branch **not** in master!\r\n\r\nIn my fork I made an update to many test cases since I changed the format, so I saved many networks in as files, they contain the current format_version (2.14.0). After merging the current version of develop I got some tests that suddenly failed eventhough my code should not mess with them. So I did a little diging and found that the expected and actual results differ in `net.res_switch_est` DataFrame. This is because the expected result only contains the old columns while the actual result contains the updated columns.\r\n\r\nThis is because the expected results are loaded form file using the `pandapower.from_json` function and since then format version is the same as the current format verison in `_version.py` the conversion to the newest format is not done. So the network is returned as loaded from file.\r\nThe actual results however are a product of a conversion from a different network type. So they are the output of a converter that creates a new pandapowerNet. These then contain all new columns.\r\n\r\nIf new columns are added `__format_version__` should be incremented at least in the bugfix number. But I would expect that this constitutes at least a minor release as a new format version most likely breaks backwards compatibility. On a bugfix version I would expect I go backwards and forwards without issue. But this is not the case if the format version changes! A 2.13.1 Network should sucessfully load on 2.13.0 but this will not work if new columns are added. So this change should be reflected by an increase of the format verison to at least 2.15.0 in my opinion.\r\n\r\nThe breaking commit is 516f8af as it changed the format without changeing the format version.\r\n\n", "before_files": [{"content": "import importlib.metadata\n\n__version__ = importlib.metadata.version(\"pandapower\")\n__format_version__ = \"2.14.0\"\n", "path": "pandapower/_version.py"}], "after_files": [{"content": "import importlib.metadata\n\n__version__ = importlib.metadata.version(\"pandapower\")\n__format_version__ = \"2.15.0\"\n", "path": "pandapower/_version.py"}]}